Non-invasive method for detecting and measuring filling material in vessels

ABSTRACT

A non-invasive method for measuring the level of filling material in a vessel and for detecting the presence of the filling material in the vessel at a predetermined set point level is based on monitoring the oscillation of the vessel&#39;s outside wall that follows an impact load applied to the external surface of the vessel&#39;s wall. The method may employ short range level measurement and long range level measurement procedures. The short-range level measurement utilizes the macro-dynamic properties of the oscillating space in the vicinity of the center of the impact. The long-range level measurement utilizes the properties of the transverse elastic waves propagating along the vessel&#39;s wall after the impact. The value of the measured level may be determined by a joint evaluation of the output of the short range level measurement procedure and the output of the long range level measurement procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority from U.S.Provisional Patent Application Ser. No. 60/532,747, filed 23 Dec. 2003,which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to methods for measuring a filling material levelin vessels and for detecting filling material presence in vessels.

2. Description of the Related Art

The need to know about the presence of a filling matter in a vessel, aswell as the quantitative information about the space that the fillingmatter occupies in the vessel, is evident in many industrial anddomestic applications. Accordingly, a variety of methods and devices aredescribed in the scientific and technical literature. Methods forfilling material level measurement could be grouped by the followingfive considerations:

-   -   1. Invasive vs. Non-invasive    -   2. Dependence of the method upon the vessel's material    -   3. Dependence of the method upon the filling material    -   4. Invariance to environmental disturbances    -   5. Safety

Of these, the primary consideration is invasive versus non-invasivebecause this consideration is the most serious constraint for themeasuring method and the measuring apparatus implementing the method.Therefore, the prior art methods will be discussed from the position ofinvasiveness first of all. Invasive methods require the presence of ameasuring device's element inside the vessel; non-invasive methods arelimited to those that do not require a measuring device's element insidethe vessel. The number of invasive methods is noticeably larger then thenumber of non-invasive methods. The former methods could utilize theprincipals of Time Domain Reflectometry of very short electrical pulses(TDR) that “ . . . are propagated along a transmission line or guidewire that is partially immersed in the material being measured. . . .Reflected pulses are produced at the material interface due to thechange in dielectric constant. . . . ” The time difference between thelaunched and reflected pulses is used to determine the material level,as disclosed in U.S. Pat. Nos. 5,610,611, 6,452,467 and 6,481,276. Thisapproach is usable in continuous and set-point level measurementapplications.

Another known approach to the material presence detection and thefilling material level measurement is based on monitoring the dynamicproperties of a mechanical system comprised of an oscillatory structuredirectly contacting the filling material as disclosed in U.S. Pat. Nos.5,631,633, 4,896,536, 6,105,425 and 5,862,431. Some solutions suggestusing a mechanical arm with one end fixed at a predetermined level andthe opposite end attached to a switch, to provide for a level relaycontrol or set point level measurement of the filling material. U.S.Pat. No. 6,111,211 issued to Dziedzic et al, serves as an example of theabove-described invasive method for the set point level measurement.Among the methods that exploit monitoring the dynamic properties of amechanical system, U.S. Pat. No. 4,954,997 issued to Dieulesaint, et al.represents a set-point liquid level measurement solution that monitorschanges in the parameters of the Lamb elastic waves in the detectionplate. These waves are generated by a transmitter and are received by areceiver of the measuring system. The plate is installed at apredetermined level inside of a tank. The parameters of the Lamb wavechange dramatically at the moment the detection plate contacts thefilling liquid, thereby allowing the set-point level measurement.Scientific Technologies, Inc., manufactures another vibrating levelsensor, VBS series. The sensor is described in the company websitewww.stiautomationproducts.com: “The VBS series is designed specificallyfor solid level detection in very small hoppers less than 3 ft (1 m)tall. The VBS is a compact diaphragm vibration switch for use with drysolids at atmospheric pressures.” “The sensitivity may vary depending onthe apparent specific gravity and fluidity of the powder,” thus thedetection sensitivity depends on the buried portion of the diaphragm inthe vertical direction.

A large group of methods is based on the capacitive properties of thefilling material. According to these methods, at least one member of themeasuring capacitor is located within the container. The electricalcapacitance of the measuring capacitor varies depending on the amount offilling material and could be calculated to correspond to the measuredlevel. U.S. Pat. Nos. 5,207,098 and 4,574,328 illustrate such invasivecapacitive methods.

Although limited by the constraints of specific applications, everyultrasound, electromagnetic, and laser method for distance measurementand their combinations are usable for measuring the filling materiallevel in vessels. Some of these methods are disclosed in U.S. Pat. Nos.5,877,997, 5,793,704, 6,122,602, 5,822,275, 5,699,151, 6,128,982 and5,892,576 and illustrate the wave-train-based invasive approaches to thevessel's filling material level measurement.

With regard to non-invasive methods for the level measurement, thefollowing popular approaches are known:

-   -   Radioactive    -   Capacitive    -   Ultrasound    -   Gravitational

Radioactive methods are based on the fact that radioactive energyattenuates after passing through a vessel's walls and through fillingmaterial. Obviously, radioactive systems are dependent on the vessel'smaterial and the filling material. These systems are not capable ofcontinuous level measurement and these systems require special designand operational efforts to maintain a sufficient degree of safety. Theexample of a radioactive system usable for a set point level measurementis Radiometric Measuring System DG57 manufactured by Endress+Hauser.

Gravitational systems require the exact knowledge of the empty vessel'sweight and its dimensions including the internal dimensions.Gravitational systems are limited in their applicability due to problemswith installation of the weight-measuring equipment and calculation ofthe actual level of filling material, which varies depending on thevessel's internal topology, mechanical properties of the fillingmaterial and environmental conditions, e.g., material viscosity ortemperature. Vishay Nobel of Sweden manufactures one such gravitationalsystem.

Non-invasive capacitive methods for the material level measurement invessels are subject to a very strong limitation. In order to obtainsatisfactory measurement resolution, the distance between the conductiveelements of a sensing capacitor must be substantially smaller than theirarea. In fact, the capacitance of two parallel rectangular plates takeninto the first approximation analysis is described by a well-knownformula:

$\begin{matrix}{C = \frac{k\; ɛ_{0}A}{d}} & (1)\end{matrix}$wherein, C denotes the capacitance; ε_(o)—electric constant; k—relativepermittivity; A—area of a flat rectangular conductive element; andd—distance between the conductive elements. Note that all mathematicalnotations in this patent application are standard (refer towww.mathworld.wolfram.com). Given that d=0.01 m, A=1.00 m², k=2.5(typical value for dielectric materials),C=2.5·8.85·10⁻¹²·1.00/0.01=22.125·10⁻⁴ μF. A 10% change in the area ofthe conductive plates results in a 221.25 pF change in the capacitance.This value is comparable with the capacitance of wiring for a printedcircuitboard. Thus, the non-invasive capacitive method for levelmeasurement is only practically applicable to very small vessels withdielectric filling material. For the same reason, in applications withelectro-conductive filling material, the non-invasive capacitive methodsare only feasible for vessels with relatively thin non-conductive walls.Therefore, non-invasive capacitive methods for the filling materiallevel measurement in vessels have a narrow field of application. U.S.Pat. Nos. 6,448,782 and 6,472,887 offer a detailed description ofdevices utilizing the non-invasive capacitive method for fillingmaterial level measurement in vessels; the former is forelectro-conductive filling material, and the later is for dielectricfilling material.

Ultrasound non-invasive methods for level measurement require theattachment of one or more transducers to the external wall of a vesselfor transmitting the acoustic energy toward the boundary surfaceseparating the filling material from the remaining space inside of thevessel. The receiver of the measuring system gets the reflectedultrasound wave train and sends it to the device's echo processingelectronics. Thus, with the exception of the external attachment of thetransducers, these methods bear all the distinctions of well-knowninvasive ultrasound methods for the distance/level measurement. However,the ultrasound non-invasive method is advantageous because of itsnon-invasiveness. At the same time, the ultrasound non-invasive approachto the filling material level measurement is limited by the homogeneityof the filling material. Typically, measuring systems of this method areused for homogeneous liquid filling materials. It is not applicable toloose materials or liquids with inclusions. In addition, this method isnot applicable to relatively small-sized containers due to problems withacoustic pulse relaxation, reverberation and the size of transducers.Plus, the method is temperature-dependent, thereby requiring temperaturecompensation during measurement. If used for the set-point levelmeasurement or material presence detection, the method is prone tocreating false alarms due to the effect of some volume of a viscousfilling material adhering to the internal surface of the container.Finally, the ultrasound-based non-invasive technologies require specialtreatment of the container's surface in order to create a conduit forultrasound waves emitted by a transducer into the container. An exampleof such technology is VesselCheck ST and SpotCheck of CannongateTechnology, UK. The VesselCheck marketing material published onwww.cannongatetechnology.co.uk says: “With VesselCheck ST, there's noneed to make holes in the vessel. The unique VesselCheck ST providescontinuous measurement with no process connections, meaning nodown-timeduring installation. Two small ultrasonic transducers are clamped to theoutside walls of the vessel. One is mounted on the bottom of the vesseland the other on the side, to compensate for variations in temperatureand density.” “SpotCheck uses an ultrasonic “footprint” to determine thepresence or absence of liquid inside a tank or pipe. . . . In order toinsure that SpotCheck will operate satisfactorily, the surface of thetank or pipe must be prepared correctly.” For instance, deseaming andgelling the wall's surface is required in the area in which thetransducer is mounted.

A similar approach has been announced by HiTECH Technologies, Inc., USA.This company markets continuous and set point devices based on theirPenetrating Pulse Technology (PPT) [Online article: “Penetrating PulseTechnology,” at www.hightechtech.com], which resembles the methoddeveloped by Cannongate Technology, Ltd., UK. The distinctive feature ofPPT is generating a single short ultrasound impulse penetrating thevessel's wall toward the filling material. The HiTECHTechnologies-developed SONOMETER for the continuous level measurementand SONOCONTROL for the set point level measurement are based on PPT.The company provides a comprehensive description of their method on thewebsite www.hitechtech.com. An analysis of PPT methods shows that thetechnology is ultrasound and uses either the Pulse Transit Time paradigmor the monitoring of the duration of ultrasound waves' relaxation toindicate the material presence in the plane in which the specialacoustical transducer is installed on the outside wall of the vessel.The PPT are subject to all of the above-described limitations of theultrasound methods of the level measurement.

An analysis of the related art shows that all known invasive ornon-invasive level measurement techniques are limited by the factors ofvessel's material, filling material and environment. See also: Burdik V.Analysis of Sonar Systems. L., 1988; Skoochik E. Fundamentals ofAcoustics. _(—)., 1976; and Krasilnikov V._., Krylov V. V. Introductionto Physical Acoustics. _(—)., 1984.

The object of the present invention is to develop a method for thenon-invasive measurement of the filling material level in the vesselfree of the underlined limitations.

SUMMARY OF THE INVENTION

A method for non-invasive evaluation of the level of filling material ina vessel is disclosed. The method may include the steps of initializingmechanical oscillation at least in a single predetermined point on theoutside wall of the vessel; performing a Close Range Level MeasurementProcedure (CRMP); performing a Long Range Level Measurement Procedure(LRMP); analyzing the outcome of the CRMP; analyzing the outcome of theLRMP; and evaluating the value of the filling material level in thevessel based on the result of the analysis of the CRMP and the LRMPoutcomes.

The method for evaluating the value of the filling material level mayinclude one of continuous measurement of the level of the fillingmaterial in the vessel, continuous monitoring the deviation of the levelof the filling material in the vessel from a set point level, set pointmeasurement of the level of the filling material in the vessel, fillingmaterial presence detection in the vessel and switching based on thelevel of the filling material.

The method may include joint performance of the CRMP and the LRMP forthe filling material level evaluation having one or more points for themechanical oscillation initiation on the external surface of the vessel.

The method may include joint performance of the CRMP and the LRMP forthe filling material level evaluation having one or more points forreceiving a mechanical oscillation on the external surface of thevessel.

The method may include measuring the value of the filling material levelin the vessel based on the analysis of the outcome of the CRMP when thepresence of the filling material in the vicinity of the point ofmechanical oscillation initiation is known.

The method may include monitoring a deviation of the level of fillingmaterial in the vicinity of the point of mechanical oscillationinitiation based on the analysis of the outcome of the CRMP.

The method may include evaluating the value of the filling material setpoint level in the vessel based on the analysis of the outcome of theCRMP.

The method may include performing the filling material level switchingin the vessel based on the analysis of the outcome of the CRMP.

The method may include performing the filling material presencedetection in the vessel based on the analysis of the outcome of theCRMP.

The method may include measuring the value of the filling material levelin the vessel based on the analysis of the outcome of the LRMP when thefilling material level is not in the vicinity of the point of themechanical oscillation initiation.

The method may include having the point of the mechanical oscillationinitiation and a point of a mechanical oscillation receiving bothlocated at one of the top of the vessel and the bottom of the vessel.

The method may include having the mechanical oscillation originatethrough a temporal mechanical load applied to an external surface of thewall of the vessel, the load being actuated by one of a solid materialbody percussion, an air-dynamic percussion, a fluid-dynamic percussion,a ballistic percussion and an electro-dynamic percussion; and a timediagram of the mechanical load having a form of one of a single pulse, atrainload of pulses and a continuous periodical load.

The method may include having the time diagram being a function of amodulation of the load, the modulation being one of an amplitudemodulation, a frequency modulation, a phase modulation, a pulse-codemodulation, a pulse-width modulation and a combination thereof, and themechanical load being originated by the transformation of a source ofdriving energy selected from one of a solenoid drive, a mechanicalenergy used in springs, a pneumatic apparatus, a hydraulic apparatus,and a ballistic percussive apparatus.

The method may include having the CRMP analyse the mechanicaloscillation obtained in at least one receiving point, the LRMP analysethe mechanical oscillation obtained in at least one receiving point, theoutcome of the CRMP being stored for consequent analysis, and theoutcome of the LRMP being stored for consequent analysis.

The method may include capturing the mechanical oscillation on theexternal surface of the wall of the vessel by the attachment ofoscillation sensing means at the point of mechanical oscillationreceiving.

The method may include capturing the mechanical oscillation on theexternal surface of the wall of the vessel by using remote oscillationsensing means at the point of mechanical oscillation receiving.

The method may include having the outcome of the CRMP include a variableor a vector of variables that allow a decision on the validity of theCRMP; the outcome of the LRMP include a variable or a vector ofvariables that allow a decision on the validity of the LRMP; theCRMP-relating variables include a vector denoted ψ_(C), and theLRMP-relating variables include a vector denoted ψ_(L).

The method may include producing evaluating binary variables of the timedomain, denoted ξ₁ and ξ₂, with the variable ξ₁ indicating the presenceor the absence of the filling material in the vicinity of the point ofmechanical oscillation initiation and with the variable ξ₂ indicatingthat the LRMP generates a valid or an invalid outcome.

The method may include using the vector ψ_(C) for the production of thevariable ξ₁ and using the vector ψ_(L) for the production of thevariable ξ₂.

The method may include having the vector ψ_(C) include a function ofamplitudes of mechanical oscillation obtained at the point of themechanical oscillation receiving, the function being defined on apredetermined time interval and the vector ψ_(C) include a function ofthe number of periods of mechanical oscillation obtained at the point ofthe mechanical oscillation receiving, and the function being defined onthe time interval.

The method may include having the CRMP control the LRMP by providinginformation on the presence or absence of the filling material in thevicinity of at least one predetermined point of mechanical oscillationinitiation.

The method may include having the value of the filling material level inthe vessel calculated by the formulas:ξ₁=0&ξ₂=0

y=f(y _(L))ξ₁=1

y=f(y _(C))L _(fm) =H−y,wherein ξ₁=0 indicates that the filling material is beyond the vicinityof the point of mechanical oscillation initiation, ξ₁=1 indicates thatthe filling material is within the vicinity of the point of mechanicaloscillation initiation, ξ₂=0 indicates that the LRMP produces a validoutcome, ξ₂=1 indicates that the LRMP produces an invalid outcome, ydenotes the distance between a point of mechanical oscillationinitiation and a filling material interface in the vessel; y_(L) denotesa level-related output of the LRMP; y_(C) denotes a level-related outputof the CRMP; L_(fm) denotes the level of filling material in the vessel;and H denotes a known height of the point of mechanical oscillationinitiation.

The method may include performing the CRMP by executing two operationswherein the first operation is an operation Calibration and the secondoperation is an operation Measurement.

The method may include having the operation Calibration include thesteps of positioning a point of mechanical oscillation initiation abovea vicinity of the material interface in the vessel; obtaining astatistical sample of the output of the CRMP by repetitively performinga Basic Measurement Procedure (BMP); deriving a value, denoted ψ₁, of anevaluating variable, denoted ψ, from the statistical sample that isassociated with an upper saturation state of a measuring system's statictransfer operator; positioning the point of mechanical oscillationinitiation below the vicinity of the filling material interface in thevessel; obtaining a statistical sample of the output of the CRMP byrepetitively performing the BMP; and deriving a value, denoted ψ₂, ofthe evaluating variable ψ, from a statistical sample that is associatedwith a lower saturation state of the measuring system's static transferoperator.

The method may further include incrementally shifting the position ofthe point of mechanical oscillation initiation toward the fillingmaterial interface in the vessel; repeating the steps disclosed in theclaim 24 after each change in the position of the point of mechanicaloscillation initiation is performed and storing the latest values of theevaluating variable ψ=ψ₁ and the distance y=y₁ between the point ofmechanical oscillation initiation and the filling material interface ifthe beginning position of the point of mechanical oscillation initiationwas above the vicinity of the filling material interface in the vesseland storing the latest values evaluating variable ψ=ψ₂ and the distancey=y₂ between the point of mechanical oscillation initiation and thefilling material interface if the beginning position of the point ofmechanical oscillation initiation was below the vicinity of the fillingmaterial interface in the vessel; and calculating parameters of anon-saturated linear static transfer operator of the measuring system bythe formulas:

$K = \frac{\psi_{1} - \psi_{2}}{y_{1\min} - y_{2\min}}$$\psi^{0} = \frac{{\left( {y_{1\min} - y_{2\min}} \right)\psi_{2}} - {y_{2\min}\left( {\psi_{1} - \psi_{2}} \right)}}{y_{1\min} - y_{2\min}}$wherein, K denotes a slope, ψ⁰ denotes an intercept of the measuringsystem's static linear transfer operator, y_(1min) denotes the minimalvalue y₁ obtained on the condition of the predetermined proximitybetween the two consequent readings of ψ₁, and y_(2min) denotes theminimal value y₂ obtained on the condition of the predeterminedproximity between the two consequent readings of ψ₂.

The operation Calibration may include the steps of positioning a pointof mechanical oscillation initiation below a vicinity of the materialinterface in the vessel; obtaining a statistical sample of the output ofthe CRMP by repetitively performing a Basic Measurement Procedure (BMP);deriving a value, denoted ψ₁, of an evaluating variable, denoted ψ, fromthe statistical sample that is associated with an lower saturation stateof a measuring system's static transfer operator; positioning the pointof mechanical oscillation initiation above the vicinity of the fillingmaterial interface in the vessel; obtaining a statistical sample of theoutput of the CRMP by repetitively performing the BMP; and deriving avalue, denoted ψ₂, of the evaluating variable ψ, from a statisticalsample that is associated with a lower saturation state of the measuringsystem's static transfer operator.

The method may include having the operation Calibration include thesteps of positioning a point of mechanical oscillation receiving above avicinity of the point of mechanical oscillation initiation; obtaining astatistical sample of the output of the CRMP by repetitively performinga Basic Measurement Procedure (BMP); deriving a value ψ₁ from astatistical sample that is associated with an upper saturation state ofa measuring system's static transfer operator; and calculating a valueψ₂, of an evaluating variable ψ by the application of a formulaψ₂=f(ψ₁), wherein, the simplest expression for f(ψ₁) is f(ψ₁)=ψ₁+δ₁; ψ₂is associated with a lower saturation state of the measuring system'sstatic transfer operator, wherein δ₁∈

—a real number.

The method may include having the operation Calibration include thesteps of positioning a point of mechanical oscillation receiving below avicinity of the point of mechanical oscillation initiation; obtaining astatistical sample of the output of the CRMP by repetitively performingBMP; deriving a value ψ₂ from the statistical sample that is associatedwith the lower saturation state of the measuring system's statictransfer operator; and calculating a value ψ₁, of an evaluating variablev by the application of a formula ψ₁=Φ(ψ₂), wherein, the simplestexpression for Φ(ψ₂) is Φ(ψ₂)=ψ₂+δ₂; ψ₁ is associated with the uppersaturation state of the measuring system's static transfer operator,wherein δ₂∈

—real number.

The method may include positioning a first point of mechanicaloscillation receiving above a vicinity of the point of mechanicaloscillation initiation; positioning a second point of mechanicaloscillation receiving below the vicinity of the point of mechanicaloscillation initiation; obtaining a statistical sample of the output ofthe CRMP by repetitively performing a Basic Measurement Procedure (BMP)in the first point of mechanical oscillation receiving and the secondpoint of mechanical oscillation receiving; deriving an evaluatingvariable from a statistical sample obtained in the first point ofmechanical oscillation receiving; deriving an evaluating variable from astatistical sample obtained in the second point of mechanicaloscillation receiving; calculating values ψ₁, ψ₂ of a measuring system'supper and lower saturation states of a measuring system's statictransfer operator according to the following formulas:∀j=(1,2):Δψ_(j)=ψ_(j)(t _(i))−ψ_(j)(t _(i−1))|Δψ_(j)−Δψ_(j)*|<ε_(j)

ψ_(j)=ψ_(j)(t _(i))wherein, j=1 denotes the first point of mechanical oscillationreceiving, j=2 denotes the second point of mechanical oscillationreceiving, i denotes the moment in time the statistical sample wasobtained, and ψ_(j) denotes the evaluating variable corresponding withthe j-th position of the point of mechanical oscillation receiving; andcalculating parameters of a non-saturated linear static transferoperator of the measuring system by the formulas:

$K = \frac{\psi_{1} - \psi_{2}}{y_{1} - y_{2}}$$\psi^{0} = \frac{{\left( {y_{1} - y_{2}} \right)\psi_{2}} - {y_{2}\left( {\psi_{1} - \psi_{2}} \right)}}{y_{1} - y_{2}}$wherein, K denotes a slope, ψ⁰ denotes an intercept of the measuringsystem's static linear transfer operator, y₁ denotes a distance betweenthe receiver and the lower point of saturation of the measuring system'sstatic transfer operator, and y₂ denotes a distance between the receiverand the upper point of saturation of the measuring system's statictransfer operator.

The method may include setting parameters of a transfer operator of ameasuring system, the parameters selected from one of ψ₁, ψ₂, y₁, y₂, K,ψ⁰ and a combination thereof.

The method may include having the operation Measurement include thesteps of performing a Basic Measurement Procedure (BMP), which output isa value of an evaluating variable ψ(t) and calculating the value of thelevel of filling material in the vessel by the formulas:Δy(t)=K ⁻¹[ψ(t)−ψ⁰]L _(fm) =f[y _(a) , Δy(t)]wherein, Δy(t) denotes a calculated distance between a filling materialinterface and a point of mechanical oscillation initiation, vector y_(a)denotes coordinates of the point of mechanical oscillation initiationpositioned on the vessel, and L_(fm) denotes the level of fillingmaterial in the vessel.

The method may include calculating the value of the level of fillingmaterial by the formula:L _(fm) =H*±Δy(t)wherein, H* denotes a known distance between the point of mechanicaloscillation initiation and the bottom of the vessel, and the arithmeticoperator “+” is used if the level of filling material is greater orequal then H* and the arithmetic operator “−” is used if the level offilling material is lower then H*.

The method may include having a Basic Measurement Procedure (BMP)include the steps of: initiating the mechanical oscillation by theapplication of a mechanical load non-tangentially aimed toward thevessel's external wall; capturing the moment in time of the mechanicaloscillation initiation; receiving a mechanical oscillation that occurson an outside surface of the wall of the vessel due to the mechanicaloscillation initiation; obtaining parameters of the mechanicaloscillation including amplitudes and frequencies corresponding with atleast some periods of the captured oscillating process; and calculatinga value of an evaluating variable denoted v by using the parameters ofthe mechanical oscillation as an input.

The method may include monitoring the parameters of the mechanicaloscillation; storing the parameter values at each moment in time theoperation Calibration is committed; comparing the monitored values ofthe parameters of the mechanical oscillation with the stored values ofthe parameters; establishing a vector, denoted as the Proximity Vector,of values reflecting the proximity between the monitored values and thestored values of the parameters of the mechanical oscillation; andexecuting the operation Calibration when components of the ProximityVector indicate that the values of the monitored parameters of themechanical oscillation are beyond a predetermined degree of proximitybetween the values of the monitored parameters of the mechanicaloscillation and the stored values of the parameters of the mechanicaloscillation.

The method may include performing the BMP more than once for the purposeof improvement of the validity of measurement.

The method may include calculating the evaluating variable's value bythe formula:

$\left. {{{\left\{ {{\forall{A_{i} \in \left\lbrack {A_{1},A_{2}} \right\rbrack}},{i = \overset{\_}{1,n}}} \right\}\&}\mspace{14mu} t} > t_{0}}\Rightarrow{\psi(t)} \right. = {n^{- 1}{\sum\limits_{i = 1}^{i = n}f_{i}}}$wherein, [A₁, A₂] denotes a predetermined amplitude range satisfying acriterion of undisturbed mechanical oscillation processing, n denotesthe number of mechanical oscillation frequencies f_(i) determined on acondition that ∀A_(i)∈[A₁, A₂], i= 1,n & t>t₀, t₀ denotes the moment oftime when the load has been applied.

The method may include calculating the evaluating variable's value bythe formula:

$\left. {{{\left\{ {{\forall{\omega_{i} \in \left\lbrack {\omega_{1},\omega_{2}} \right\rbrack}},{i = \overset{\_}{1,m}}} \right\}\&}\mspace{14mu} t} > t_{0}}\Rightarrow{\psi(t)} \right. = \left. {\sum\limits_{i = 1}^{i = m}{\sin\left( T_{i} \right)}} \right|_{A_{i} \in {\lbrack{A_{1},A_{2}}\rbrack}}$wherein, [ω₁, ω₂] denotes a frequency range satisfying a criterion ofnon-generation of mechanical elastic waves, T_(i) denotes an i-th fullperiod of oscillation observed beginning at a moment t₀.

The method may include providing for a high repeatability and highaccuracy of measurement, and further including:

${\psi(t)} = {q^{- 1}{\sum\limits_{i = 1}^{i = q}{b_{i}{\psi_{i}(t)}}}}$wherein, ψ_(i)(t) denotes the evaluating variable obtained by an i-thexecution of the BMP, and b_(i) denotes a weighting factor correspondingwith the i-th execution of the BMP.

The method may include evaluating variable ψ_(i)(t) as one of a functionof amplitudes of mechanical oscillation obtained at the point of themechanical oscillation receiving over a predetermined time interval, afunction of the number of periods of mechanical oscillation obtained atthe point of the mechanical oscillation receiving over a predeterminedtime interval, and a function of the presence or absence of the fillingmaterial in the vicinity of a predetermined point of mechanicaloscillation initiation.

The method may include monitoring mechanical oscillations in at leasttwo different points on the surface of the vessel, wherein these pointsare consequently denoted p₁, p₂, . . . , p_(r) with the r denoting thenumber of the points; and forming the evaluating variable ψ(t) based onthe output from each point for mechanical oscillation receiving.

The method may include providing two points for mechanical oscillationreceiving and further include calculating the evaluating variable ψ(t)by the following formulas:y _(p1)(t _(i))=K ⁻¹[ψ_(p1)(t)−ψ⁰]y _(p2)(t _(i))=K ⁻¹[ψ_(p2)(t)−ψ⁰]y _(p1)(t _(i))−y _(p2)(t _(i))=const

ψ(t)=f[ψ _(p1)(t), ψ_(p2)(t)]wherein, y_(p1), y_(p2) denote a distance from each point p₁, p₂ to afilling material interface.

The method may include applying a series of mechanical loads to thevessel's external wall per each measurement such that each applicationof the mechanical load is a percussion; generating the evaluatingvariable per each percussion in the series; validating eachpercussion-associated evaluating variable such that each evaluatingvariable is considered either valid or invalid; creating an array of thevalid evaluating variables per each series of percussions; selectingthose arrays that have a length greater or equal to a predeterminednumber; statistically treating each array for the purpose ofdetermination of the presence or the absence of the filling material inthe vicinity of the point for mechanical oscillation initiation; forminga binary status variable of the discrete time domain, denoted s(t), thatindicates the presence or absence of the filling material in thevicinity of the point for mechanical oscillation initiating; andincluding the status variable into a vector-output of the CRMP.

The method may include statistically processing each array of validevaluating variables by an application of a Major Algorithm.

The method may include forming the binary status variable by theformulas:∀t _(i) , i= 1 ,r:ψ(t _(i))∈ψ_(valid)

y(t _(i))=K ⁻¹[ψ(t _(i))−ψ⁰]s(t)=F[ψ(t ₁),ψ(t ₂), . . . , ψ(t _(r)), t]wherein, F[ ] denotes a function of the evaluating variables.

The method may include calculating the function F[ ] according to theformula:

${F\left\lbrack {{\psi\left( t_{1} \right)},{\psi\left( t_{2} \right)},\ldots\mspace{14mu},{\psi\left( t_{r} \right)},t} \right\rbrack} = {r^{- 1}{\sum\limits_{i = 1}^{i = r}{{\psi\left( t_{i} \right)}.}}}$

The method may include performing a set-point level measurement by meansof the CRMP with a modified operation Measurement.

The method may include having the modified operation Measurement includethe following steps: performing a Basic Measurement Procedure (BMP),which output is the value of an evaluating variable ψ(t) obtained at themoment of time the BMP has been committed; and calculating a statusvariable s(t) relating to the level of filling material in the vessel bythe following formulas:∀ψ(t)>0, ∃s(t):ψ(t)−ψ_(1s)>0

s(t)=“Filling material is below the level set point”ψ(t)−ψ_(2s)<0

s(t)=“Filling material is above the level set point”wherein, the parameters denoted ψ_(1s), ψ_(2s) define a dead zone of theset-point measurement.

The method may include having the dead zone parameters ψ_(1s) and ψ_(2s)being functions of saturation points ψ₁ and ψ₂.

The method may include associating a value denoted ψ′_(S), of anevaluating variable with a known value of a binary status variable;calculating a value denoted ψ″_(s), of the evaluating variable that isassociated with the opposite binary outcome of the status variable suchthat s(ψ″_(S))=

s(ψ′_(s)); storing the values ψ′_(s) and ψ″_(s) for further use in theoperation Measurement in the set point level measurement applicationsand for a material presence detection in the vicinity of the level setpoint and in level switching applications; and updating the valuesψ′_(s) and ψ″_(s) according to a schedule of execution of the BMP.

The method may include applying the CRMP to more than one point on theexternal wall of the vessel and executing a repetitive CRMP (RCRMP),such that the level of the filling material is measured at severalpoints.

The method may further include locating a plurality of points along avertical axis on the external wall of the vessel; applying a BasicMeasurement Procedure (BMP) sequentially to each point of the pluralityof points beginning from a starting position on the vessel's externalwall toward an ending position on the vessel's external wall until thefollowing condition is satisfied:∃j∈[1,m]⊂

:ψ_(j)(t)∈(ψ*₁,ψ*₂)

ψ(t)=ψ_(j)(t),wherein, ψ_(j)(t) denotes an evaluating variable for a j-th execution ofthe BMP; ψ*₁, ψ*₂ and K* respectively denote upper and lower saturationpoints and a gain factor of an aggregated transfer operator of adistributed measuring system or device; and calculating the level by thefollowing formulas:y*=(ψ*₁−ψ*₂)/K*y _(j)(t)=[ψ(t)−ψ⁰ ]/K*y(t)=(j−1)y*±y _(j)(t)L _(fm) =H−y(t)

starting position is in the upper half of vesselL _(fm) =y(t)

starting position is in the lower half of vesselwherein, y* denotes a spread distance corresponding with a linear partof the distributed measuring system's transfer operator; H denotes aheight of the starting position, and the “+” in the “±” sign is for astarting point located in a lower half of the vessel and the “−” in the“±” sign is for a starting point located in an upper half of the vessel.

The method may include locating a plurality of points along a verticalaxis on the external wall of the vessel; applying a Basic MeasurementProcedure (BMP) simultaneously to at least two points of the pluralityof points beginning from a starting position on the vessel's externalwall toward an ending position on the vessel's external wall anddetecting the ordering number of the point, for which the followingcondition is satisfied:∃j∈[1,m]⊂

:ψ_(j)(t)∈(ψ*₁,ψ*₂)

ψ(t)=ψ_(j)(t);and calculating the evaluating variable's value by the formula:

$\left. {{{\left\{ {{\forall{\omega_{i} \in \left\lbrack {\omega_{1},\omega_{2}} \right\rbrack}},{i = \overset{\_}{1,m}}} \right\}\&}\mspace{14mu} t} > t_{0}}\Rightarrow{\psi(t)} \right. = \left. {\sum\limits_{i = 1}^{i = m}{\sin\left( T_{i} \right)}} \right|_{A_{i} \in {\lbrack{A_{1},A_{2}}\rbrack}}$wherein, [ω₁, ω₂] denotes a frequency range satisfying a criterion ofnon-generation of mechanical elastic waves, T_(i) denotes an i-th fullperiod of oscillation observed beginning at a moment t₀.

For applications with a multi-layer structure of the filling material,having layers of a different density, to measure dimensions of eachlayer of the multi-layer structure in the vessel, the method may includeapplying a repetitive CRMP (RCRMP).

The method may include, prior to initializing the mechanicaloscillation, mounting elements on the vessel's wall for setting boundaryconditions for mechanical oscillation-induced elastic waves propagatingin the vessel, to define a linear part of a level measurement system'sstatic transfer operator.

The method may include receiving at least one acoustical signaloriginated by an application of at least one percussion within asequence of operations of a Basic Measurement Procedure (BMP) andcalculating an evaluating variable resulting from the BMP using ameasured mechanical oscillation and a measured acoustical signalassociated with the mechanical oscillation.

The method may include performing the LRMP by executing two operationswherein the first operation is an operation of calibration and thesecond operation is an operation of measurement.

The operation of calibration for the LRMP may include the steps of:setting an initial value of the filling material level in the vessel;non-tangentially applying the mechanical oscillation to the vessel'sexternal wall at a predetermined point to initiate a transverse wave;capturing an occurrence of the transverse wave at a predeterminedtransverse wave receiving point; and measuring and storing the value ofa time interval denoted ΔT* between the moment of the transverse waveinitiation and the moment of the wave occurrence capturing, such thatthe time interval ΔT* is associated with a distance between the point oftransverse wave initiation and the filling material interface, denotedy*.

The operation of measurement for the LRMP may include the steps of:non-tangentially applying the mechanical oscillation to the vessel'sexternal wall at a point of a transverse wave initiation; capturing anoccurrence of the transverse wave at a predetermined transverse wavereceiving point; measuring and storing a value of a time intervaldenoted ΔT between the moment of the transverse wave initiation and themoment of the wave occurrence capturing, such that the time interval ΔTis associated with a distance between the point of transverse waveinitiation and the filling material interface, denoted y; andcalculating the measured level denoted L_(fm), by the formulas:

$y = {\frac{\Delta\; T}{\Delta\; T^{*}} \cdot y^{*}}$ L_(fm) = H − y − dwherein, d denotes a known distance between a top of the vessel and thepoint of transverse wave initiation.

Performing the LRMP may include the steps of: arranging for monitoring apresence of a transverse wave at a plurality of receiving points on theexternal wall of the vessel to compensate for possible variations inpropagation speed of the monitored waves through the material of thevessel's wall; non-tangentially applying the mechanical oscillation tothe vessel's external wall at the point of a transverse wave initiation;capturing the transverse wave's presence at each wave's receiving pointof the plurality of points; measuring and storing each value of a timeinterval denoted ΔT_(i) between a moment of the transverse waveinitiation and a moment of the wave capturing at an i-th point of theplurality of points, such that each time interval ΔT_(i) is associatedwith a distance between the i-th receiving point and the fillingmaterial interface, denoted y_(i); and calculating the level by solvingthe following system of algebraic equations of the order m:F(L _(fm) , H, ΔT, d)=0wherein, L_(fm) denotes the level of filling material in the vessel; Hdenotes a height of the vessel; ΔT denotes a vector of time intervalsbetween the moment of the transverse wave initiation and the moment thewave capturing at the i-th point of the plurality of points; d denotes aknown distance between a top of the vessel and the point of transversewave initiation; m denotes the number of the transverse wave receivingpoints.

The method may include calculating the measured level by the followingformulas:

$y = {\frac{\Delta\; T}{{\overset{\_}{\Delta\; T}}^{*}} \cdot \overset{\_}{y^{*}}}$$y^{*} = {n^{- 1}{\sum\limits_{i = 1}^{i = n}{\overset{\_}{y_{i}}}^{*}}}$wherein, y* and ΔT* denote an aggregated calibrating distance and anaggregated calibrating wave travel time obtained by monitoring thewave's responses captured at n receiving points of the plurality of thetransverse wave receiving points and ΔT represents the transverse wave'stravel time along the wall of the vessel.

The method may include having an evaluating variable ψ_(L)∈ψ_(L)generated by the LRMP include a variable ΔT, representing the transversewave's travel time along the wall of the vessel, the evaluating variableψ_(L) being a function of the variable ΔT, such that ψ_(L)=F(ΔT), and afiltering or aggregation or statistical processing is applied to obtainthe evaluating variable for the LRMP.

The method may include calculating the variable ΔT by the formula:

${\Delta\; T} = {m^{- 1}{\sum\limits_{j = 1}^{j = m}{\Delta\; T_{j}}}}$wherein, ΔT_(j) denotes a travel time obtained at j-th measurement inthe series of m measurements.

The method may also include providing a first impact load at apredetermined load point on an external wall of the vessel to initializea first oscillation in the wall of the vessel and in the fillingmaterial in the vessel; receiving a measure of the first oscillation ata first predetermined receiving point; analyzing the measure of thefirst oscillation received at the first predetermined receiving point todetermine a first evaluating variable; and determining a level of thefilling material in the vessel based on the first evaluating variable.

These and other objects, features and advantages of the presentinvention will become apparent in light of the drawings and detaileddescription of various embodiments of the present invention providedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic of the method implementing system of oneembodiment of the present invention with in-plane positioning of thestriker and the receiver and with the filling material interface belowthe center of impact;

FIG. 1 b is a schematic of the method implementing system of anotherembodiment of the present invention with coaxial positioning of thestriker and the receiver;

FIG. 2 depicts a simplified non-linear dynamic spring-mass modelassociated with the Close Range Level Measuring Procedure of the methodof the present invention;

FIG. 3 shows a vertical section of a pipe partially filled with amaterial;

FIG. 4 shows a non-linear static transfer characteristic of the testedmeasuring system of FIG. 3;

FIG. 5 a depicts an oscillogram of mechanical oscillations in theexperimental setting of FIG. 3 for a fiberglass pipe of 3.175 cm (1.25inches) diameter and 3 mm wall thickness filled with water;

FIG. 5 b depicts an oscillogram of mechanical oscillations in theexperimental setting of FIG. 3 for an empty fiberglass pipe of 3.175 cm(1.25 inches) diameter and 3 mm wall thickness;

FIG. 6 a depicts an oscillogram of mechanical oscillations for a pipefilled with water, showing time, frequency and amplitude; and

FIG. 6 b depicts an oscillogram of mechanical oscillations for an emptypipe, showing time, frequency and amplitude.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method of the present invention is based on monitoring theoscillatory motion of the vessel's outside wall; such motion, forexample, being initiated by the application of a mechanical loaddirected at the wall.

In one aspect, the method utilizes a Close Range Level MeasuringProcedure (CRMP) to non-invasively measure the level of the fillingmaterial within a vessel. CRMP exploits the properties of the mechanicaldynamic system that includes the wall of the vessel and the fillingmaterial near the load point. At a relatively short distance between theload point and the filling material's interface, the oscillation of themechanical dynamic system, i.e. the “instantaneous associate fillingmaterial mass and the instantaneous associate vessel's wall(s) mass,” isused to obtain the level of the filling material measurement.

In another aspect, the method utilizes a Long Range Level MeasuringProcedure (LRMP) to measure the level of the filling material. LRMPexploits an elastic waves-based approach for the distance measurement.

In even another aspect, the method of the present invention provides forautomatically switching from the CRMP output to the LRMP output, andvise versa, while producing the measurement. The decision on whichprocedure's output contributes to a valid level reading depends on ajoint evaluation of the output of CRMP and the output of LRMP. Thedeveloped method may be a sequence of the following steps:

-   -   1. initializing vibration at at least a single predetermined        position on the vessel's outside wall;    -   2. substantially simultaneously performing CRMP and LRMP;    -   3. evaluating the output of CRMP and the output of LRMP; and    -   4. calculating the value of the filling material level in the        vessel based on the result of the joint evaluation of the CRMP        and LRMP outputs.        Below, each step of the proposed method is described in detail        for the method's minimal version of a single source of        vibration.

Step 1 includes initializing vibration at at least a singlepredetermined position on the vessel's outside wall. The vibration mayoriginate in the neighborhood of a mechanical impact with its centerlocated on the outside wall of the vessel. The impact load's timediagram could be of various forms including a single pulse, a trainloadof pulses or a continuous periodical load. Each impact load-type of Step1 may utilize any kind of modulation, for example, Amplitude Modulation,Frequency Modulation, Pulse-Code Modulation or their combinations. Theparticular realization of the vibration-generating load depends on themethod's measurement procedures (LRMP/CRMP). A mechanical impact at thewall could be originated by the application of any suitable energysource depending on the technical requirements of the particularmeasurement project. Examples of impact sources include, but are notlimited to, a solenoid, a spring, a hydraulic and an air pressure-baseddrive.

Step 2 includes substantially simultaneously performing CRMP and LRMP. Amechanical vibration captured by the receiver of the measuring system isthe input for CRMP and for LRMP. Each procedure executes independently.The output of CRMP and the output of LRMP are used jointly to determinethe control variable of the method.

Step 3 includes evaluating the output of CRMP and the output of LRMP.The CRMP output and the LRMP output, which are used for the evaluation,could be a procedure-relating variable or a vector of variables thatallow a decision on the sensitivity of the procedure to be made. Let theCRMP-relating variables compose a vector denoted ψ_(C) and theLRMP-relating variables compose a vector denoted ψ_(L). The evaluationof the outputs ψ_(C) and ψ_(L) includes the production of binaryevaluating variables ξ₁ and ξ₂ such that:∀t∈[t ₁ , t ₂], ∃ξ₁∈_(—){0,1}, ξ₂∈_(—){0,1}:ψ_(C)⊂Ψ_(Ce)

ξ₁=0, “Absent”ψ_(C)⊂Ψ_(Cf)

ξ₁=1, “Present”ψ_(L)⊂Ψ_(Lv)

ξ₂=0, “Valid reading”ψ_(L)⊂Ψ_(Ln)

ξ₂=1, “Invalid reading”  (2)wherein, Ψ_(Ce), denotes the subset of the CRMP-relating vectors ψ_(C)that are associated with the absence of the filling matter in thevicinity of the center of the impact; Ψ_(Cf), denotes the subset of theCRMP-relating vectors ψ_(C) that are associated with the presence of thefilling matter in the vicinity of the center of the impact; Ψ_(Lv)denotes the subset of the LRMP-relating vectors ψ_(L) that areassociated with a valid distance measurement between the receiver andthe filling material interface; Ψ_(Ln) denotes the subset of theLRMP-relating vectors ψ_(L) that are associated with an invalid distancemeasurement between the receiver and the filling material interface.

Step 4 includes calculating the value of the filling material level inthe vessel based on the result of the joint evaluation of the CRMP andLRMP outputs. In order to calculate the value of the measured level, themethod of the present invention requires knowledge of the distancebetween the receiver of vibration and the filling material interface;the distance being denoted y. Once the distance y is obtained, the levelof the filling material, denoted L_(fm), is derivable by the subtractionof this distance from the known height, denoted H, of the receiver'sposition on the vessel's wall. The distance y obtained by the executionof the CRMP is denoted y_(C). The distance y obtained by the executionof the LRMP is denoted y_(L). Based on the above definitions, the valueof the filling material level in the vessel can be calculated asfollows:ξ₁=0 & ξ₂=0

y=y _(L)ξ₁=1

y=y _(C)  (3)L _(fm) =H−y.Close Range Level Measurement Procedure (CRMP)

The Close Range Level Measurement Procedure emerged from a study ofdynamic macro processes in the Associate Filling Material Mass andAssociate Vessel's Wall(s) Mass system conducted by the authors of thepresent invention. The term “Associate” reflects the observation thatthe amount of matter involved in the oscillating process following amechanical impact to the vessel's wall is limited and that it depends onthe mechanical energy dissipation in the space surrounding the center ofthe impact. The space surrounding the center of the impact includes thewall(s) of the vessel and the matter inside the vessel. Also, this spaceincludes the body of any mechanical source of the impact and the body ofa sensing element if the former is used in some method's application forthe mechanical oscillation initiation and the latter is used in othermethod's application for the mechanical oscillation receiving by beingattached to the outside wall of the vessel. It is not critical to themethod of the present invention that the source of the impact has amechanical origin. Also, it is not critical to the method of the presentinvention that the sensing element is attached to the wall of thevessel. However, for the sake of generalization, it will be furtherassumed that a time-dependent mechanical load is applied to the vessel'soutside wall by a small moving body of mass m_(s); such moving bodybeing called a “Striker”. Additionally, it will be assumed that thesensing element that receives the mechanical oscillations resulting fromthe impact is attached to the vessel's external surface and that it hasa mass m_(r).

A mechanical sketch of the studied system is shown in FIG. 1 a and FIG.1 b. In FIG. 1 a, a vessel 16 having a wall contains filling material12. A striker 18 is shown contacting the external surface of the wall ofthe vessel. The striker has a mass, m_(s). A receiver 20 is shownattached to the external surface of the wall of the vessel. The receiverhas a mass, m_(r). The effective associate mass of the matter that fillsthe excited space surrounding the center of impact of striker 18 isdenoted as item 10. The center of the impact is denoted as a dashedline. The arrows denote the distance between the center of impact andthe filling material interface. In FIG. 1 b, receiver 20 is shownaligned with striker 18.

The system's simplified spring-mass model is presented in FIG. 2. Inthis model, C₁ denotes the stiffness of the leg between mass m_(s) andmass m_(e); m_(e) denotes the associate effective mass of the matterthat fills the excited space surrounding the center of the impact. Thevalue of m_(e) depends on the container's geometry, the density of thewall(s) and density of the matter inside the space involved in theoscillating process. The value of m_(e) also depends on the amount ofmechanical energy induced into the filling material through the wall. C₂denotes the stiffness of the leg between mass m_(r) and mass m_(e). β₁and β₂ denote damping coefficients in parallel with stiffnesses C₁ andC₂, respectively.

A substantial non-linearity of the model may arise, on one hand, by thepossibility of losing a mechanical contact between the striker and thevessel's wall and, on the other hand, by the possibility of losing amechanical contact between the vessel's wall and the receiver ofmechanical oscillations. In addition, non-linearity may arise due to theviolation of the mechanical medium continuity of the filling materialitself, for example, a granulated material. The above-mentionednon-linearity is reflected in the spring-mass model of FIG. 2 in theform of two parallel lines, item 22, attached to the beginning end ofeach spring 24. The dimensions of the excited space and the energyrelaxation property of the filling matter have a strong inverserelationship, such that the higher the mechanical energy dissipation ofthe filling material, the smaller the dimensions of the space involvedin the mechanical oscillation. Another important observation is that thefilling matter typically is comprised of two major components: gaseousand non-gaseous. In many industrial applications, the gaseous componentis air and the non-gaseous component is fluid or loose/solid materialwith air-filled gaps between solid kernels. Examples of such loosematerial include cotton web or balls, PVC pellets or seeds.

The amount of the oscillating matter within a container is associatedwith the center of the impact and it effectively depends on the level ofthe filling material and the type of the material. For example, considerthe vessel 16 to be a pipe 26 of internal diameter 2·r and wallthickness δ; such a vessel is depicted in FIG. 3. FIG. 3 shows avertical section of pipe 26 partially filled with a material 12 and air28. The position of the center of impact 14 and all geometricaldimensions of the pipe and the filling material needed for the reasoningof the effective associated mass concept are shown on the drawing. Ananalysis of the dynamics of the mechanical system shown in FIG. 3 hasled to the conclusion that the amount of oscillating matter within acontainer is associated with the center of the impact and that iteffectively and non-ambiguously depends on the level of the fillingmaterial and the type of the filling material. The effective mass m_(e)may be described by the following formulas:m _(e) =m _(w) +m _(a) +m _(f);h _(e) =h _(a) +h _(f);m _(w)=ρ_(w) V _(w) , V _(w) =πδh(2r+δ);m _(a)=ρ_(a) V _(a)(h _(a));  (4)m _(f)=ρ_(f) V _(f)(h _(f));wherein, m_(w), m_(a), and m_(f) respectively denote the mass of thepipe's material, the mass of the air within the pipe relating to theimpact-induced oscillating process and the mass of the filling materialwithin the pipe relating to the impact-induced mechanical oscillatingprocess; V_(w), V_(a) and V_(f) respectively denote the volume of thepipe's material, the volume of the air within the pipe relating to theimpact-induced oscillating process and the volume of the fillingmaterial within the pipe relating to the impact-induced mechanicaloscillating process; ρ_(w), ρ_(a) and ρ_(f) respectively denote thedensity of the pipe's material, the density of the air and the densityof the filling material, which is considered homogeneous for the sake ofsimplicity of the method's disclosure; h denotes the height of the partof the pipe relating to the impact-induced oscillating process; h_(a)denotes the part of the height h associated with the air within the piperelating to the impact-induced oscillating process; h_(f) denotes thepart of the height h associated with the filling material within thepipe relating to the impact-induced oscillating process.

By taking into consideration that m_(a)<<m_(f), one can conclude thatthe effective associate mass m_(e) is directly proportional to theheight h_(f). This reasoning supports the notion that the level of thefilling material in the pipe or in any other vessel is measurablethrough the monitoring of mechanical oscillations originated by animpact to the vessel's wall if the filling material interface ispositioned within the distance of ±h_(e) from the center of the impact.

The above-discussed example was MathCAD computed with the help of the3-mass spring-mass model, shown in FIG. 2. The model's parameters wereas follows:

-   -   Pipe material—fiberglass or steel    -   Diameter, internal—2.54 mm    -   Length—600 mm    -   Wall thickness—3 mm    -   Filling material—water

The result of the modeling was evaluated using the ratio η=ω₁/ω₂ of thenatural frequencies of a single pulse-load relaxation process obtainedwith an empty pipe (ω₁) and a pipe filled with water (ω₂). In this case,η=1.5. A comparison of the modeled data with data obtained from ourexperiments with fiberglass and metal pipes of similar dimensions andunder similar conditions, FIG. 1 b, showed 12% proximity between bothsets of data. The important observation from the modeling and from theexperimental data was that the natural frequency-related evaluatingvariable was lower in the pipe filled with water than the empty pipe.The explanation to this phenomenon is based on the following reasoning.The mass m_(a) of air involved in the pipe's transverse oscillatingprocess following the mechanical impact, is several orders of magnitudesmaller than the mass m_(fl) of water occupying the space in theneighborhood of the center of the impact and participating in theoscillating process. Because fluid keeps mechanical contact with thewalls of the fluid-holding vessel (under a no cavitation condition), thecombined mass of the studied oscillating system with water will behigher than the mass of this system without water. This results in thereduction of the dominant frequency of the studied mechanical system.

Filling the pipe with a granulated material causes the opposite effect:the dominant frequency of the studied mechanical system rises relativeto the dominant frequency of the excited empty pipe. The physicalexplanation of this observed phenomenon is complex and requires theanalysis of the studied mechanical system under the conditions of adisruption of the mechanical medium and a high degree of mechanicalenergy dissipation typical in loose materials [Yavorski B. M., Detlaf A.A., Physics Handbook. Moscow, Nauka, 1990; Earth's Crust Research:Geophysical Methods; Overview: www.astronet.ru, Nov. 21, 2003; OlshevskyB. M. Statistical Methods in Hydro Ranging. L., 1983; Yakovlev _. _.,_blov G. P. Short Range Sonars. L., 1983; and Golubkov _. G. CustomizedSonar Systems. L., 1987].

Due to a significant stiffness of the pipe's wall, a relatively smallpart of the pipe is involved in the oscillating process initiated by theimpact. Accordingly, the value h, FIG. 3, delimits the space where thefilling matter oscillates after the impact, thus the value of h limitsthe value of the effective mass m_(e). When the pipe is filled with agranulated material, a certain amount of granules collide with theoscillating wall at every moment of existence of the oscillatingprocess, thereby increasing the frequency and the logarithmic decrementof the observed mechanical oscillations on the outside surface of thevessel's wall. A number of the granules do not oscillate due to a highmutual friction between the granules creating an “Oscillon” phenomenonand reducing the effective oscillating space including the pipe wallsand the filling material and increasing the frequency of oscillations,respectively. Besides this, the presence of the compressed granulatedmaterial in the vicinity of the impact makes that portion of theoscillating space immobile, thereby creating an effect of the rigidattachment that causes the mechanical system oscillate at higherfrequencies. Thus, a combination of different physical processes in theoscillating system of the granulation-filled vessel causes a repeatableobservable effect: an increase in the dominant frequency of the vessel'swall mechanical oscillations accompanied by a decrease in the dominantoscillation's logarithmic decrement.

The fact that the natural frequency of the excited pipe unambiguouslydepends on the type of filling material effectively improves theapplicability of the method of the present invention.

The range of frequencies measured on the experimental installationdepicted in FIG. 1 b, lay within the interval 1200–2000 Hz. Due to thefact that all observations were made on multiple periods of themonitored signal, the presence of acoustical standing waves could beviewed as a possible alternative explanation to the observed phenomenon.However, by taking into account the average value of the speed of soundpropagating through air, water and granulated materials [Earth's CrustResearch: Geophysical Methods; Overview: www.astronet.ru, Nov. 21, 2003;and Mark's Standard Handbook for Mechanical Engineers, Tenth Edition.Eugene A. Avallone and Theodore Baumeister 3^(rd): McGraw-Hill, NY], itwas determined that the predicted value of the acoustical standing wavesfrequencies in our experimental installation do not fall within theabove-identified interval [John William Strutt, the 3rd Baron Rayleigh.The Theory of Sound. _(—)., 1955]:f=c _(m)/2xwherein c_(m) denotes the speed of sound in the medium; and x denotesthe distance to the first of the wave antinodes. With x=25.4 mm, thefollowing acoustical standing wave frequencies were calculated:

-   -   Case 1: Pipe is empty.        -   c_(a)=331.8 m/s, f=6,531.5 Hz.    -   Case 2: Pipe filled with water.        -   c_(fl)=1461.0 m/s, f=28,759.8 Hz.    -   Case 3: Pipe filled with granulated material        -   c_(g)=500.0–1,000.0 m/s, f=9,842.5–19,685.1 Hz.

The value of the effective height h_(e) is not constant. It depends onmany factors in addition to those that have already been discussed. Infact, h_(e) is a random variable, as is the effective mass m_(e). Thestochastic nature of the instantaneous effective mass in the studiedmechanical system complicates the level measurement. In order to improvethe accuracy and repeatability of this measurement, we have equipped themeasuring system with two brackets (not shown). The brackets createpredictable and stable boundary conditions for mechanical oscillationsin the vicinity of the center of the impact. In the tested embodiment,these brackets had the shape of a half-pipe cut along the pipe'slongitudinal axis. Each bracket had a length of 150 mm. The use of thebrackets secured the repeatability and the accuracy of measurement andprovided for the linearity of the level measurement. The static transferoperator obtained for the tested embodiment is a linear function withsaturation at h*≈±L_(b), L_(b) denotes the length of the bracket. Thestatic transfer characteristic of the tested measuring system is shownin FIG. 4. In general, FIG. 4 shows a typical non-linear static transfercharacteristic obtained by the method of the present invention of asystem wherein the diameter of the vessel is substantially smaller thanthe length of the vessel.

The above-discussed theoretical and experimental research has led to thecreation of the inventive non-invasive procedure for measuring thefilling material level in vessels. A detail description of CRMP follows,which includes several possible embodiments of calculating the value ofthe evaluating variable.

CRMP includes two major operations: calibration and measurement.Calibration includes the following five steps. (To simplify mathematicalnotations, beginning here, the subscript “c” of the variable ψ_(c) willbe omitted.)

-   a. Step-by-step performing Basic Measurement Procedure (BMP)    beginning from the filling material's interface positioned at the    center of the impact to the filling material's interface distanced    from the center of the impact toward the bottom of the vessel. The    output of each BMP is the value of the evaluating variable, denoted    ψ(y), which is directly and unambiguously linked to the position of    the filling material's interface relative to the center of the    impact. The distance from the center of the impact to the filling    material interface is denoted y.-   b. Recording the value ψ₁=ψ(y₁) of the evaluating variable that is    associated with the beginning of the lower saturation state of the    measuring system's static transfer operator.-   c. Step-by-step performing BMP beginning from the filling material's    interface positioned at the center of the impact to the filling    material's interface distance from the center of the impact toward    the top of the vessel.-   d. Recording the value ψ₂=ψ(y₂) of the evaluating variable that is    associated with the beginning of the upper saturation state of the    measuring system's static transfer operator.-   e. Calculating parameters of the measuring system's non-saturated    linear static transfer operator using the following formulas:

$\begin{matrix}{K = \frac{\psi_{1} - \psi_{2}}{y_{1} - y_{2}}} & (9) \\{\psi^{0} = \frac{{\left( {y_{1} - y_{2}} \right)\psi_{2}} - {y_{2}\left( {\psi_{1} - \psi_{2}} \right)}}{y_{1} - y_{2}}} & (10)\end{matrix}$wherein, K denotes the slope and ψ⁰ denotes the intercept of themeasuring system's static linear transfer operator.

The measurement operation for CRMP includes the following two steps:

-   a. Performing BMP, which output is the value of the evaluating    variable ψ(t) obtained at the moment t of time the BMP has been    committed.-   b. Calculating the level of the filling material in the vessel by    the following formulas:    y(t)=K ⁻¹[ψ(t)−ψ⁰]  (11)    L _(fm) =H−y(t)  (12)    wherein, y(t) denotes the calculated distance between the filling    material interface and the receiver in the case of a coaxial    positioning of the center of the impact and the receiver (see FIG. 1    b); and H denotes the height of the center of impact; L_(fm) denotes    the level of the filling material in the vessel.

Both the above-enumerated calibration and measurement operations of CRMPutilize a Basic Measurement Procedure (BMP). BMP includes the followingfour steps:

-   a. applying an impact load toward the vessel's external wall    surface, such that the direction of the impact is not tangent to the    vessel's external wall surface, passing through the center of the    impact and indicating the moment of impact;-   b. receiving a mechanical vibration that occurs on the external    surface of the wall because of the impact;-   c. measuring primary parameters of the vibration, including, for    instance, amplitudes and frequencies, after implementing a    predetermined delay from the moment of the impact; and-   d. calculating the value of the evaluating variable using the    vibration primary parameters as input.

Various variables may be selected to serve as the evaluating variablethat is calculated in step (d) of the BMP. In a first embodiment, theevaluation variable ψ(t) may be the average of the frequencies within apredetermined amplitude range:

$\begin{matrix}{\left. {{{\left\{ {{\forall{A_{i} \in \left\lbrack {A_{1},A_{2}} \right\rbrack}},{i = \overset{\_}{1,n}}} \right\}\&}\mspace{14mu} t} > t_{0}}\Rightarrow{\psi(t)} \right. = {n^{- 1}{\sum\limits_{i = 1}^{i = n}f_{i}}}} & (13)\end{matrix}$wherein, [A₁, A₂] denotes a predetermined amplitude range satisfying thecriterion of undisturbed vibration processing; n denotes the number ofvibration frequencies f_(i) determined on condition that ∀A_(i)∈[A₁,A₂], i=1,n & t>t₀; t₀ denotes the moment of time when the load has beenapplied.

In a second embodiment, the evaluation variable may be the summation ofthe sine of the full periods of oscillation within a predeterminedfrequency range.

$\begin{matrix}{\left. {{{\left\{ {{\forall{\omega_{i} \in \left\lbrack {\omega_{1},\omega_{2}} \right\rbrack}},{i = \overset{\_}{1,m}}} \right\}\&}\mspace{14mu} t} > t_{0}}\Rightarrow{\psi(t)} \right.\mspace{200mu} = \left. {\sum\limits_{i = 1}^{i = m}{\sin\left( T_{i} \right)}} \right|_{A_{i} \in {\lbrack{A_{1},A_{2}}\rbrack}}} & (14)\end{matrix}$wherein, [ω₁, ω₂] denotes a predetermined frequency range satisfying thecriterion of the mechanical standing waves non-generation; m denotes thenumber of full periods of oscillation determined on condition that{∀ω_(i)∈[ω₁, ω₂], i=1,m} & t>t₀; and T_(i) denotes the i-th full periodof oscillation observed beginning the moment t₀.

In a third embodiment, the combined use of different evaluatingvariables, e.g., variable ψ_(m1)(t)=ψ(t) from expression (13) andvariable ψ_(m2)(t)=ψ(t) from expression (14) allows the improvement ofthe repeatability and accuracy of the measurement. In the general case,this measurement approach may be described with the help of thefollowing expression:

$\begin{matrix}{{\psi(t)} = {q^{- 1}{\sum\limits_{i = 1}^{i = q}{b_{mi}{\psi_{mi}(t)}}}}} & (15)\end{matrix}$wherein, ψ_(mi)(t) denotes the evaluating variable obtained by the i-thimplementation of BMP; b_(mi) denotes a weighting factor correspondingwith the i-th implementation of BMP; and q denotes the number ofimplementations of BMP. The values of the weighing factors depend on thetechnical application the method is being applied.

In a fourth embodiment, mechanical oscillations in at least twodifferent points on the external surface of the vessel may be monitored.These points are denoted p₁, p₂, . . . p_(r), with r denoting the numberof these points. This approach also improves the accuracy andrepeatability of the measurement. In this embodiment, the calculation ofthe evaluating variable includes output from each receiver positioned ineach point p_(i), i= 1,r. In the particular case of two receiversmounted in two separate points p₁ and p₂, the validation of theevaluating variable can be based on the criterion of constancy of thedifference between the measured distances y_(p1), y_(p2) from each pointto the filling material interface. Thus, only valid ψ(t) are used forthe measured level calculation:y _(p1)(t _(i))=K ⁻¹[ψ_(p1)(t)−ψ⁰]y _(p2)(t _(i))=K ⁻¹[ψ_(p2)(t)−ψ⁰]  (16)y _(p1)(t _(i))−y _(p2)(t _(i))=const

ψ(t)=F[ψ _(p1)(t), ψ_(p2)(t)].

According to a fifth embodiment, a substantial increase in the accuracyand repeatability of the level measurement is also achievable by theapplication of more than one impact load to the vessel's wall permeasurement. In this case, the method of the present invention requires:

-   a. calculating the evaluating variable per each impact and storing    its value for further processing as an element of the series of    evaluating variables;-   b. statistically treating the obtained series of evaluating    variables and selecting at least one valid series;-   c. determining the fact of the filling material presence or absence    within the vicinity of the center of impact per each impact;-   d. applying a Major Algorithm to each valid series of evaluating    variables for the determination of the presence or absence of the    filling material in the vicinity of the center of impact;-   e. forming a status variable indicating the presence or absence of    the filling material in the vicinity of the center of impact and    having the status variable as the CRMP output in the case of a    set-point level measurement or the material presence detection at    the set-point level; and-   f. having the status variable indicating the presence of the filling    material in the vicinity of the center of impact, and calculating    the valid series-relating evaluating variable by the formulas:    ∀t _(i) , i=1,r:    ψ(t _(i))∈ψ_(valid)    y(t _(i))=K ⁻¹[ψ(t _(i))−ψ⁰]    ψ(t)=F[ψ(t ₁), ψ(t ₂), . . . , ψ(t _(r)), t]    wherein, F[ ] denotes a function defined on the evaluating variables    in the valid series, which output is the CRMP's resulting evaluating    variable. In one possible embodiment, the ψ(t) variable may be    calculated with the help of an aggregating function, such that:

$\begin{matrix}{{F\left\lbrack {{\psi\left( t_{1} \right)},{\psi\left( t_{2} \right)},\ldots\mspace{14mu},{\psi\left( t_{r} \right)},t} \right\rbrack} = {r^{- 1}{\sum\limits_{i = 1}^{i = r}{\psi\left( t_{i} \right)}}}} & (17)\end{matrix}$

In formula (17), F[ ] denotes the aggregating function defined on theset of evaluating variables obtained at each i-th impact in the validsequence of r impacts.

In light of the above explanation, it can be seen that the set pointlevel measurement is a particular case of the continuous levelmeasurement. The set point level measurement can be attained by means ofCRMP with unchanged BMP and a modified operation measurement as follows:

-   a. performing BMP, which output is the value of the evaluating    variable ψ(t) obtained at the moment t of time the BMP has been    committed; and-   b. calculating the status variable on the level of the filling    material in the vessel by the following formulas:    ∀ψ(t)>0, ε₁>0, ε₂>0, ∃s(t):    |ψ(t)−ψ_(1s)|<ε₁    s(t)=“Filling material is below the level set point”    |ψ(t)−ψ_(2s)|>ε₂    s(t)=“Filling material is above the level set point”    wherein, the method's predetermined dead zone parameters denoted    ψ_(1s) and ψ_(2s) are functions of the saturation points ψ₁ and ψ₂;    s(t) denotes the status variable. In the simplest case, the    saturation points could be calculated as follows: ψ_(1s)=b₁ψ₁ and    ψ_(2s)=b₂ψ₂, where b1, b2 are predetermined coefficients. The    condition |ψ(t)−ψ_(1s)|=ε₁ or |ψ(t)−ψ_(2s)|=ε₂ could be attributed    to any binary value of the status variable s(t) depending on the    technical specification of the application of the method.

It is clear that a multitude of forms is available for theimplementation of the evaluating variable ψ(t) and the status variables(t) in continuous and set point measurement applications includingthose described by expressions (13)–(18). However, all members of thepopulation of evaluating and status variables correspond with the ideaand the scope of the method of the present invention. The evaluatingvariables that were defined in the formulas (13)–(18) may serve ascomponents of the vector ψ_(c) in the integral description of the methodof the present invention; refer to the expression (2).

FIGS. 5 a and 5 b depict sample oscillograms of mechanical oscillationsfor a fiberglass pipe filled with water and an empty pipe, respectively.FIG. 6 a and FIG. 6 b provide illustrative examples of forming theevaluating variable ψ(t) with the help of the oscillogram of mechanicaloscillations in the above-described experimental setting with thefiberglass pipe. From FIG. 6 a, for a pipe filled with water, thefollowing values can be determined: f₁=1.538 KHz, f₂=1.538 KHz, andf₃=1.0 KHz, and the evaluating variable calculated: ψ=(f₁+f₂+f₃)/3=1.304KHz. From FIG. 6 b, for an empty pipe, the following values can bedetermined: f₁=1.429 KHz, f₂=5.5 KHz, f₃=1.538 KHz, and f₄=1.25 KHz, andthe evaluating variable calculated: ψ=(f₁+f₂+f₃+f₄)/4=1.5686 KHz.

The execution of CRMP at more than one point on the outside wall of thevessel allows the level measurement beyond the vicinity of the center ofthe impact. In such case, the level of the filling material is measuredin m points simultaneously or sequentially depending on the method'simplementation. Both of these realizations of the method are based onthe observation that the evaluating variable ψ(t) will change oncondition that the filling material interface is located in the vicinityof one of m possible centers of impact. In other words, due to thesaturation property of the measuring systems' static transfer operator:ψ_(j)(t)≈ψ_(1j) or ψ_(j)(t)≈ψ_(2j)ψ_(1j)→ψ*₁, ψ_(2j)→ψ*₂, j= 1,qwherein, q≦m is due to the saturation property of the measuring systems'static transfer operator; and ψ*₁, ψ*₂ are the upper and low saturationparameters, respectively, of the aggregated static transfer operator ofthe distributed system.

The method for the remote level measurement is based on the repetitiveexecution of CRMP, denoted RCRMP, and is realizable by a distributedmeasuring system. After an initial calibration, the distributedmeasuring system may utilize either a sequential method or a parallelmethod to determine the measured level. The sequential method mayinclude the following sequence of operations:

-   a. installing a single measuring system capable of originating and    monitoring wall's oscillation at m predetermined points along the    vertical axis of the vessel;-   b. beginning at a predetermined starting position on the vessel's    outside wall, proceed with a step-by-step application of BMP until    the following condition is satisfied:    ∃j∈[1,m]⊂    :ψ_(j)(t)∈(ψ*₁,ψ*₂)    ψ(t)=ψ_(j)(t); and-   c. calculating the measured level by the following formulas:    y*=(ψ*₁−ψ*₂)/K*    y _(j)(t)=[ψ(t)−ψ⁰ ]/K*    y(t)=(j−1)y*±y _(j)(t)    L _(fm) =H−y(t)    wherein, ψ*₁, ψ*₂ and K* respectively denote the upper and lower    saturation points and the gain factor of the aggregated transfer    operator of the distributed measuring system implementing RCRMP; y*    denotes the spread distance corresponding with the linear part of    the measuring system's transfer operator; H denotes the height of    the starting position for the measuring system; in the formula for    the calculation of the y(t), the “+” in the “±” sign is for the    starting point located at the bottom of the vessel and the “−” in    the “±” sign is for the starting point located at the top of the    vessel.

The parallel method may include the following sequence of operations:

-   a. installing a plurality of measuring systems for originating and    monitoring the wall's vibration in certain predetermined points    along the vertical axis of the vessel;-   b. substantially simultaneous applying BMP and determining the    ordering number of the device, for which condition (19) is    satisfied; and-   c. calculating the measured level using formula (20) where H denotes    the height of the receiver's position for the first measuring    system.

In addition to the remote level measurement, the utilization of thedistributed system implementing RCRMP in applications with a multiplayerstructure of the filling material having layers of different densitymakes possible material profiling during measurement.

Long Range Level Measurement Procedure

A Long Range Level Measurement Procedure (LRMP) has also been developed.LRMP is based on the notion that some elastic waves, includingtransverse waves propagating along the vessel's wall, will be reflectedat the point of the medium's discontinuity [Karl F. Graff. Wave Motionin Elastic Solids. Oxford: Clarendon Press, 1975]. In the levelmeasurement applications, such discontinuity could be due to the fillingmaterial attaching to the wall's inside surface. A transverse wavetraveling along the vessel's wall meets the discontinuity at the heightof the filling material interface and will be reflected back to thereceiver. Therefore, the reflected waves deliver information regardingthe level of the filling material in the vessel. Given thisunderstanding, LRMP could employ any prior art distance measuring methodincluding, but not limited to, pulse-based and continuousecho-processing techniques such as the Pulse Transit Time Method, PhaseDifference Method, and Amplitude Change Method as disclosed in U.S. Pat.Nos. 5,793,704, 5,822,275, 5,877,997, 6,040,898 and 6,166,995 and othervery sophisticated methods developed for seismic analyses [Note Online:Refraction Seismic Methods. www.mines.edu].

LRMP will be described below with the assumption that the measurementtechnique is based on the Pulse Transit Time paradigm. This techniqueseems to be particularly suitable for vessels with heights greater than1.0 meter. LRMP can be implemented as a two-step procedure or as aone-step procedure.

The two-step LRMP includes two major operations—calibration andmeasurement. Calibration may be accomplished by the following two steps:

-   1. in the vessel with the known distance denoted y* between the    filling material interface and the receiver of vibration, applying a    mechanical load toward the vessel's external wall surface such that    the direction of the impact is not a tangent passing through the    center of the impact and indicating the moment of the impact; and-   2. monitoring the reflected wave, measuring and storing the value of    the time interval, ΔT*, between the moment of the impact and the    moment the response to the impact has been indicated, such that the    time interval ΔT* is unambiguously associated with the distance y*.

Measurement for the two-step LRMP may be accomplished by the followingthree steps:

-   1. applying a mechanical load toward the vessel's external wall    surface such that the direction of the impact is not a tangent    passing through the center of the impact and indicating the moment    of the impact;-   2. monitoring the reflected wave, measuring and storing the value of    the time interval between the moment of the impact and the moment    the response to the impact has been indicated; and-   3. calculating the measured level by the following formulas:

$\begin{matrix}{{y = {\frac{\Delta\; T}{\Delta\; T^{*}} \cdot y^{*}}}{L_{fm} = {H - y}}} & (21)\end{matrix}$wherein, H denotes the distance between the center of the impact and thebottom of the vessel.

The one-step LRMP may be accomplished by the following four steps:

-   1. installing one or more additional receiver(s) of vibration at one    or more predetermined distance(s) from the center of the impact to    compensate for possible variations in the speed of the monitored    waves propagation through the material of the vessel's wall.    Therefore, the measuring system implementing the method is equipped    with one master receiver and with at least one compensating    receiver;-   2. applying a mechanical load toward the vessel's external wall    surface such that the direction of the impact is not a tangent    passing through the center of the impact and indicating the moment    of the impact;-   3. substantially simultaneously monitoring the reflected waves by    means of measuring and storing the value of the time interval    between the moment of the impact and the moment the response to the    impact has been indicated by the master (ΔT) and the compensating    receiver(s) (ΔT*); and-   4. calculating the measured level by the formulas (19) for one    compensating receiver by the following formulas:    f(ΔT,y)=0;  (22a)    f(ΔT*,y*)=0, |ΔT*|=n, |y*|=n;  (22b)    L _(fm) =H−y  (22c)    wherein, the first equation, (22a), represents the relationship    between the distance from the master receiver and the filling    material interface; the second equation, (22b), represents the    relationship between the distances from a plurality of compensatory    receivers and the filling material interface. The above system of    equations demonstrates one of several well-known approaches to the    determination of a physical variable with the use of compensatory    measuring devices and serves for the purpose of illustration.

In the particular case of the known distance y* and the measurabletransit time ΔT* provided by the compensatory receiver, the levelmeasurement could be obtained by the following formulas:

$y = {\Delta\;{T \cdot \frac{y^{*}}{\Delta\; T^{*}}}}$ L_(fm) = H − yfor one compensating receiver or by the following formulas for more thanone compensating receiver in the measuring system:

$y = {\Delta\;{T \cdot \frac{\overset{\_}{y^{*}}}{{\overset{\_}{\Delta\; T}}^{*}}}}$${{\overset{\_}{y}}^{*} = {n^{- 1}{\sum\limits_{i = 1}^{i = n}y_{i}^{*}}}},{{\overset{\_}{\Delta\; T}}^{*} - {n^{- 1}{\sum\limits_{i = 1}^{i = n}{\Delta\; T_{i}^{*}}}}}$L_(fm) = H − yWherein, y* and ΔT* denote the aggregated calibrating distance and theaggregated calibrating wave travel time obtained with the help of ncompensating receivers in the measuring system. It is clear that anykind of filtering or aggregation is applicable to the output of LRMP.The variable ΔT in the formulas (21) and (23) plays the same role as theevaluating variable ψ(t) that was defined in the CRMP. Thus for the sakeof better accuracy and repeatability of measurement, according to onepossible embodiment, ΔT can be calculated as follows:

$\begin{matrix}{{\Delta\; T} = {m^{- 1}{\sum\limits_{j = 1}^{j = m}{\Delta\; T_{j}}}}} & (24)\end{matrix}$wherein, ΔT_(j) denotes the travel time obtained at the j-th measurementin the series of measurements of number m. The method of aggregationdepends on the particular application for which the proposed method isbeing used and is not limited to formula (24). The evaluating variablesthat were defined in the formulas (21), (23) and (24) may serve ascomponents of the vector ψ_(L) in the integral description of the methodof the present invention; refer to expression (2).

The above-disclosed method provides for a truly non-invasive measurementof a filling material level in a variety of vessels regardless of thevessel's dimensions and the vessel's material, as well as regardless ofthe physical properties of the filling matter. In addition, the presentinvention may be utilized to determined other physical parameters orproperties of the filling material which have an effect on themechanical oscillations of the system, including, for example, thedensity of the filling material.

Although the present invention has been described with respect to thedetailed embodiments presented herein, it will be understood by thoseskilled in the art that various changes in form or detail thereof may bemade without departing from the spirit and scope of the presentinvention.

1. A method for non-invasive evaluation of the level of filling materialin a vessel, comprising the steps of: initializing mechanicaloscillation at least in a single predetermined point on the outside wallof the vessel; performing a Close Range Level Measurement Procedure(CRMP); performing a Long Range Level Measurement Procedure (LRMP);analyzing the outcome of the CRMP; analyzing the outcome of the LRMP;and evaluating the value of the filling material level in the vesselbased on the result of the analysis of the CRMP and the LRMP outcomes.2. A method as claimed in claim 1, wherein evaluating the value of thefilling material level includes one of continuous measurement of thelevel of the filling material in the vessel, continuous monitoring thedeviation of the level of the filling material in the vessel from a setpoint level, set point measurement of the level of the filling materialin the vessel, filling material presence detection in the vessel andswitching based on the level of the filling material.
 3. A method asclaimed in claim 1, further including: joint performance of the CRMP andthe LRMP for the filling material level evaluation having one or morepoints for the mechanical oscillation initiation on the external surfaceof the vessel.
 4. A method as claimed in claim 1, further including:joint performance of the CRMP and the LRMP for the filling materiallevel evaluation having one or more points for receiving a mechanicaloscillation on the external surface of the vessel.
 5. A method asclaimed in claim 1, further including: measuring the value of thefilling material level in the vessel based on the analysis of theoutcome of the CRMP when the presence of the filling material in thevicinity of the point of mechanical oscillation initiation is known. 6.A method as claimed in claim 1, further including: monitoring adeviation of the level of filling material in the vicinity of the pointof mechanical oscillation initiation based on the analysis of theoutcome of the CRMP.
 7. A method as claimed in claim 1, furtherincluding: evaluating the value of the filling material set point levelin the vessel based on the analysis of the outcome of the CRMP.
 8. Amethod as claimed in claim 1, further including: performing the fillingmaterial level switching in the vessel based on the analysis of theoutcome of the CRMP.
 9. A method as claimed in claim 1, furtherincluding: Performing the filling material presence detection in thevessel based on the analysis of the outcome of the CRMP.
 10. A method asclaimed in claim 1, further including: measuring the value of thefilling material level in the vessel based on the analysis of theoutcome of the LRMP when the filling material level is not in thevicinity of the point of the mechanical oscillation initiation.
 11. Amethod as claimed in claim 1, wherein the point of the mechanicaloscillation initiation and a point of a mechanical oscillation receivingare both located at one of the top of the vessel and the bottom of thevessel.
 12. A method as claimed in claim 1, wherein the mechanicaloscillation originates through a temporal mechanical load applied to anexternal surface of the wall of the vessel, the load being actuated byone of a solid material body percussion, an air-dynamic percussion, afluid-dynamic percussion, a ballistic percussion and an electro-dynamicpercussion; and a time diagram of the mechanical load has a form of oneof a single pulse, a trainload of pulses and a continuous periodicalload.
 13. A method as claimed in claim 12, wherein the time diagram is afunction of a modulation of the load, the modulation being one of anamplitude modulation, a frequency modulation, a phase modulation, apulse-code modulation, a pulse-width modulation and a combinationthereof, and the mechanical load is originated by the transformation ofa source of driving energy selected from one of a solenoid drive, amechanical energy used in springs, a pneumatic apparatus, a hydraulicapparatus, and a ballistic percussive apparatus.
 14. A method as claimedin claim 1, wherein the CRMP analyses the mechanical oscillationobtained in at least one receiving point, the LRMP analyses themechanical oscillation obtained in at least one receiving point, theoutcome of the CRMP is stored for consequent analysis, and the outcomeof the LRMP is stored for consequent analysis.
 15. A method as claimedin claim 14, further including: capturing the mechanical oscillation onthe external surface of the wall of the vessel by the attachment ofoscillation sensing means at the point of mechanical oscillationreceiving.
 16. A method as claimed in claim 14, further including:capturing the mechanical oscillation on the external surface of the wallof the vessel by using remote oscillation sensing means at the point ofmechanical oscillation receiving.
 17. A method as claimed in claim 1,wherein the outcome of the CRMP includes a variable or a vector ofvariables that allow a decision on the validity of the CRMP, the outcomeof the LRMP includes a variable or a vector of variables that allow adecision on the validity of the LRMP; the CRMP-relating variablesinclude a vector denoted ψ_(C), and the LRMP-relating variables includea vector denoted ψ_(L).
 18. A method as claimed in claim 17, furtherincluding: producing evaluating binary variables of the time domain,denoted ξ₁ and ξ₂, with the variable ξ₁ indicating the presence or theabsence of the filling material in the vicinity of the point ofmechanical oscillation initiation and with the variable ξ₂ indicatingthat the LRMP generates a valid or an invalid outcome.
 19. A method asclaimed in claim 18, further including: using the vector ψ_(C) for theproduction of the variable ξ₁ and; using the vector ψ_(L) for theproduction of the variable ξ₂.
 20. A method as claimed in claim 19,wherein the vector ψ_(C) includes a function of amplitudes of mechanicaloscillation obtained at the point of the mechanical oscillationreceiving, the function is defined on a predetermined time interval andthe vector ψ_(C) includes a function of the number of periods ofmechanical oscillation obtained at the point of the mechanicaloscillation receiving, and the function is defined on the time interval.21. A method as claimed in claim 10, wherein the CRMP controls the LRMPby providing information on the presence or absence of the fillingmaterial in the vicinity of at least one predetermined point ofmechanical oscillation initiation.
 22. A method as claimed in claim 21,wherein the value of the filling material level in the vessel iscalculable by the formulas:ξ₁=0 & ξ₂=0

y=f(y _(L))ξ₁=1

y=f(y _(C))L _(fm) =H−y, wherein ξ₁=0 indicates that the filling material is beyondthe vicinity of the point of mechanical oscillation initiation, ξ₁=1indicates that the filling material is within the vicinity of the pointof mechanical oscillation initiation, ξ₂=0 indicates that the LRMPproduces a valid outcome, ξ₂=1 indicates that the LRMP produces aninvalid outcome, y denotes the distance between a point of mechanicaloscillation initiation and a filling material interface in the vessel;y_(L) denotes a level-related output of the LRMP; y_(C) denotes alevel-related output of the CRMP; L_(fm) denotes the level of fillingmaterial in the vessel; and H denotes a known height of the point ofmechanical oscillation initiation.
 23. A method as claimed in claim 1,further including: performing the CRMP by executing two operationswherein the first operation is an operation Calibration and the secondoperation is an operation Measurement.
 24. A method as claimed in claim23, wherein the operation Calibration includes the steps of: positioninga point of mechanical oscillation initiation above a vicinity of thematerial interface in the vessel; obtaining a statistical sample of theoutput of the CRMP by repetitively performing a Basic MeasurementProcedure (BMP); deriving a value, denoted ψ₁, of an evaluatingvariable, denoted ψ, from the statistical sample that is associated withan upper saturation state of a measuring system's static transferoperator; positioning the point of mechanical oscillation initiationbelow the vicinity of the filling material interface in the vessel;obtaining a statistical sample of the output of the CRMP by repetitivelyperforming the BMP; and deriving a value, denoted ψ₂, of the evaluatingvariable ψ, from a statistical sample that is associated with a lowersaturation state of the measuring system's static transfer operator. 25.A method as claimed in claim 24, further including: incrementallyshifting the position of the point of mechanical oscillation initiationtoward the filling material interface in the vessel; repeating the stepsdisclosed in the claim 24 after each change in the position of the pointof mechanical oscillation initiation is performed and storing the latestvalues of the evaluating variable ψ=ψ₁ and the distance y=y₁ between thepoint of mechanical oscillation initiation and the filling materialinterface if the beginning position of the point of mechanicaloscillation initiation was above the vicinity of the filling materialinterface in the vessel and storing the latest values evaluatingvariable ψ=ψ₂ and the distance y=y₂ between the point of mechanicaloscillation initiation and the filling material interface if thebeginning position of the point of mechanical oscillation initiation wasbelow the vicinity of the filling material interface in the vessel; andcalculating parameters of a non-saturated linear static transferoperator of the measuring system by the formulas:$K = \frac{\psi_{1} - \psi_{2}}{y_{1\min} - y_{2\min}}$$\psi^{0} = \frac{{\left( {y_{1\min} - y_{2\min}} \right)\psi_{2}} - {y_{2\min}\left( {\psi_{1} - \psi_{2}} \right)}}{y_{1\min} - y_{2\min}}$wherein, K denotes a slope, ψ⁰ denotes an intercept of the measuringsystem's static linear transfer operator, y_(1min) denotes the minimalvalue y₁ obtained on the condition of the predetermined proximitybetween the two consequent readings of ψ₁, and y_(2min) denotes theminimal value y₂ obtained on the condition of the predeterminedproximity between the two consequent readings of ψ₂.
 26. A method asclaimed in claim 23, wherein the operation Calibration includes thesteps of: positioning a point of mechanical oscillation initiation belowa vicinity of the material interface in the vessel; obtaining astatistical sample of the output of the CRMP by repetitively performinga Basic Measurement Procedure (BMP); deriving a value, denoted ψ₁, of anevaluating variable, denoted ψ, from the statistical sample that isassociated with an lower saturation state of a measuring system's statictransfer operator; positioning the point of mechanical oscillationinitiation above the vicinity of the filling material interface in thevessel; obtaining a statistical sample of the output of the CRMP byrepetitively performing the BMP; and deriving a value, denoted ψ₂, ofthe evaluating variable N, from a statistical sample that is associatedwith a lower saturation state of the measuring system's static transferoperator.
 27. A method as claimed in claim 23, wherein the operationCalibration includes the steps of: positioning a point of mechanicaloscillation receiving above a vicinity of the point of mechanicaloscillation initiation; obtaining a statistical sample of the output ofthe CRMP by repetitively performing a Basic Measurement Procedure (BMP);deriving a value ψ₁ from a statistical sample that is associated with anupper saturation state of a measuring system's static transfer operator;and calculating a value ψ₂, of an evaluating variable ψ by theapplication of a formula ψ₂=f(ψ₁), wherein, the simplest expression forf(ψ₁) is f(ψ₁)=ψ₁+δ₁; ψ₂ is associated with a lower saturation state ofthe measuring system's static transfer operator, wherein δ₁∈

—a real number.
 28. A method as claimed in claim 23, wherein theoperation Calibration includes the steps of: positioning a point ofmechanical oscillation receiving below a vicinity of the point ofmechanical oscillation initiation; obtaining a statistical sample of theoutput of the CRMP by repetitively performing BMP; deriving a value ψ₂from the statistical sample that is associated with the lower saturationstate of the measuring system's static transfer operator; andcalculating a value ψ₁, of an evaluating variable ψ by the applicationof a formula ψ₁=Φ(ψ₂), wherein, the simplest expression for Φ(ψ₂) isΦ(ψ₂)=ψ₂+δ₂; ψ₁ is associated with the upper saturation state of themeasuring system's static transfer operator, wherein δ₂∈

—real number.
 29. A method as claimed in claim 23, further including:positioning a first point of mechanical oscillation receiving above avicinity of the point of mechanical oscillation initiation; positioninga second point of mechanical oscillation receiving below the vicinity ofthe point of mechanical oscillation initiation; obtaining a statisticalsample of the output of the CRMP by repetitively performing a BasicMeasurement Procedure (BMP) in the first point of mechanical oscillationreceiving and the second point of mechanical oscillation receiving;deriving an evaluating variable from a statistical sample obtained inthe first point of mechanical oscillation receiving; deriving anevaluating variable from a statistical sample obtained in the secondpoint of mechanical oscillation receiving; calculating values ψ₁, ψ₂ ofa measuring system's upper and lower saturation states of a measuringsystem's static transfer operator according to the following formulas:∀j=(1,2): Δψ_(j)=ψ_(j)(t _(i))−ψ_(j)(t _(i−1))|Δψ_(j)−Δψ_(j)*|<ε_(j)

ψ_(j)=ψ_(j)(t _(i)) wherein, j=1 denotes the first point of mechanicaloscillation receiving, j=2 denotes the second point of mechanicaloscillation receiving, i denotes the moment in time the statisticalsample was obtained, and ψ_(j) denotes the evaluating variablecorresponding with the j-th position of the point of mechanicaloscillation receiving; and calculating parameters of a non-saturatedlinear static transfer operator of the measuring system by the formulas:$K = \frac{\psi_{1} - \psi_{2}}{y_{1} - y_{2}}$$\psi^{0} = \frac{{\left( {y_{1} - y_{2}} \right)\psi_{2}} - {y_{2}\left( {\psi_{1} - \psi_{2}} \right)}}{y_{1} - y_{2}}$wherein, K denotes a slope, ψ⁰ denotes an intercept of the measuringsystem's static linear transfer operator, y₁ denotes a distance betweenthe receiver and the lower point of saturation of the measuring system'sstatic transfer operator, and y₂ denotes a distance between the receiverand the upper point of saturation of the measuring system's statictransfer operator.
 30. A method as claimed in claim 1, furtherincluding: setting parameters of a transfer operator of a measuringsystem, the parameters selected from one of ψ₁, ψ₂, y₁, y₂, K, ψ⁰ and acombination thereof.
 31. A method as claimed in claim 23, wherein theoperation Measurement includes the steps of: performing a BasicMeasurement Procedure (BMP), which output is a value of an evaluatingvariable ψ(t); and calculating the value of the level of fillingmaterial in the vessel by the formulas:Δy(t)=K ⁻¹[ψ(t)−ψ⁰]L _(fm) =f[y _(a) , Δy(t)] wherein, Δy(t) denotes a calculated distancebetween a filling material interface and a point of mechanicaloscillation initiation, vector y_(a) denotes coordinates of the point ofmechanical oscillation initiation positioned on the vessel, and L_(fm)denotes the level of filling material in the vessel.
 32. A method asclaimed in claim 31, further including: calculating the value of thelevel of filling material by the formula:L _(fm) =H*±Δy(t) wherein, H* denotes a known distance between the pointof mechanical oscillation initiation and the bottom of the vessel, andthe arithmetic operator “+” is used if the level of filling material isgreater or equal then H* and the arithmetic operator “−” is used if thelevel of filling material is lower then H*.
 33. A method as claimed inclaim 23, wherein a Basic Measurement Procedure (BMP) includes the stepsof: initiating the mechanical oscillation by the application of amechanical load non-tangentially aimed toward the vessel's externalwall; capturing the moment in time of the mechanical oscillationinitiation; receiving a mechanical oscillation that occurs on an outsidesurface of the wall of the vessel due to the mechanical oscillationinitiation; obtaining parameters of the mechanical oscillation includingamplitudes and frequencies corresponding with at least some periods ofthe captured oscillating process; and calculating a value of anevaluating variable denoted ψ by using the parameters of the mechanicaloscillation as an input.
 34. A method as claimed in claim 33, furtherincluding: monitoring the parameters of the mechanical oscillation;storing the parameter values at each moment in time the operationCalibration is committed; comparing the monitored values of theparameters of the mechanical oscillation with the stored values of theparameters; establishing a vector, denoted as the Proximity Vector, ofvalues reflecting the proximity between the monitored values and thestored values of the parameters of the mechanical oscillation; andexecuting the operation Calibration when components of the ProximityVector indicate that the values of the monitored parameters of themechanical oscillation are beyond a predetermined degree of proximitybetween the values of the monitored parameters of the mechanicaloscillation and the stored values of the parameters of the mechanicaloscillation.
 35. A method as claimed in claim 33, further including:performing the BMP more than once for the purpose of improvement of thevalidity of measurement.
 36. A method as claimed in claim 35, furtherincluding: calculating the evaluating variable's value by the formula:$\left. {{{\left\{ {{\forall{A_{i} \in \left\lbrack {A_{1},A_{2}} \right\rbrack}},{i = \overset{\_}{1,n}}} \right\}\&}\mspace{14mu} t} > t_{0}}\Rightarrow{\psi(t)} \right. = {n^{- 1}{\sum\limits_{i = 1}^{i = n}f_{i}}}$wherein, [A₁, A₂] denotes a predetermined amplitude range satisfying acriterion of undisturbed mechanical oscillation processing, n denotesthe number of mechanical oscillation frequencies f_(i) determined on acondition that ∀A_(i)∈[A₁, A₂], i= 1,n & t>t₀, t₀ denotes the moment oftime when the load has been applied.
 37. A method as claimed in claim35, further including: calculating the evaluating variable's value bythe formula:$\left. {{{\left\{ {{\forall{\omega_{i} \in \left\lbrack {\omega_{1},\omega_{2}} \right\rbrack}},{i = \overset{\_}{1,m}}} \right\}\&}\mspace{14mu} t} > t_{0}}\Rightarrow{\psi(t)} \right. = \left. {\sum\limits_{i = 1}^{i = m}{\sin\left( T_{i} \right)}} \right|_{A_{i} \in {\lbrack{A_{1},A_{2}}\rbrack}}$wherein, [ω₁, ω₂] denotes a frequency range satisfying a criterion ofnon-generation of mechanical elastic waves, T_(i) denotes an i-th fullperiod of oscillation observed beginning at a moment t₀.
 38. A method asclaimed in claim 35, providing for a high repeatability and highaccuracy of measurement, further including:${\psi(t)} = {q^{- 1}{\sum\limits_{i = 1}^{i = q}{b_{i}{\psi_{i}(t)}}}}$wherein, ψ_(i)(t) denotes the evaluating variable obtained by an i-thexecution of the BMP, and b_(i) denotes a weighting factor correspondingwith the i-th execution of the BMP.
 39. A method as claimed in claim 38,further including: evaluating variable ψ_(i)(t) as one of a function ofamplitudes of mechanical oscillation obtained at the point of themechanical oscillation receiving over a predetermined time interval, afunction of the number of periods of mechanical oscillation obtained atthe point of the mechanical oscillation receiving over a predeterminedtime interval, and a function of the presence or absence of the fillingmaterial in the vicinity of a predetermined point of mechanicaloscillation initiation.
 40. A method as claimed in claim 35, furtherincluding: monitoring mechanical oscillations in at least two differentpoints on the surface of the vessel, wherein these points areconsequently denoted p₁, p₂, . . . , p_(r) with the r denoting thenumber of the points; and forming the evaluating variable ψ(t) based onthe output from each point for mechanical oscillation receiving.
 41. Amethod as claimed in claim 40, wherein two points for mechanicaloscillation receiving are provided, further including: calculating theevaluating variable ψ(t) by the following formulas:y _(p1)(t _(i))=K ⁻¹[ψ_(p1)(t)−ψ⁰]y _(p2)(t _(i))=K ⁻¹[ψ_(p2)(t)−ψ⁰]y _(p1)(t _(i))−y _(p2)(t _(i))=const

ψ(t)=f[ψ_(p1)(t), ψ_(p2)(t)] wherein, y_(p1), y_(p2) denote a distancefrom each point p₁, p₂ to a filling material interface.
 42. A method asclaimed in claim 23, further including: applying a series of mechanicalloads to the vessel's external wall per each measurement such that eachapplication of the mechanical load is a percussion; generating theevaluating variable per each percussion in the series; validating eachpercussion-associated evaluating variable such that each evaluatingvariable is considered either valid or invalid; creating an array of thevalid evaluating variables per each series of percussions; selectingthose arrays that have a length greater or equal to a predeterminednumber; statistically treating each array for the purpose ofdetermination of the presence or the absence of the filling material inthe vicinity of the point for mechanical oscillation initiation; forminga binary status variable of the discrete time domain, denoted s(t), thatindicates the presence or absence of the filling material in thevicinity of the point for mechanical oscillation initiating; andincluding the status variable into a vector-output of the CRMP.
 43. Amethod as claimed in claim 42, further including: statisticallyprocessing each array of valid evaluating variables by an application ofa Major Algorithm.
 44. A method as claimed in claim 42, furtherincluding: forming the binary status variable by the formulas:∀t _(i) , i= 1,r:ψ(t _(i))∈ψ_(valid)

y(t _(i))=K ⁻¹[ψ(t _(i))−ψ⁰]s(t)=F[ψ(t ₁), ψ(t ₂), . . . , ψ(t _(r)), t] wherein, F[ ] denotes afunction of the evaluating variables.
 45. A method as claimed in claim44, further including: calculating the function F[ ] according to theformula:${F\left\lbrack {{\psi\left( t_{1} \right)},{\psi\left( t_{2} \right)},\ldots\mspace{14mu},{\psi\left( t_{r} \right)},t} \right\rbrack} = {r^{- 1}{\sum\limits_{i = 1}^{i = r}{{\psi\left( t_{i} \right)}.}}}$46. A method as claimed in claim 23, further including: performing aset-point level measurement by means of the CRMP with a modifiedoperation Measurement.
 47. A method as claimed in claim 46, wherein: themodified operation Measurement includes the following steps: performinga Basic Measurement Procedure (BMP), which output is the value of anevaluating variable ψ(t) obtained at the moment of time the BMP has beencommitted; and calculating a status variable s(t) relating to the levelof filling material in the vessel by the following formulas:∀ψ(t)>0, ∃s(t):ψ(t)−ψ_(1s)>0

s(t)=“Filling material is below the level set point”ψ(t)−ψ_(2s)<0

s(t)=“Filling material is above the level set point” wherein, theparameters denoted ψ_(1s), ψ_(2s) define a dead zone of the set-pointmeasurement.
 48. A method as claimed in the claim 47, wherein the deadzone parameters ψ_(1s) and ψ_(2s) are functions of saturation points ψ₁and ψ₂.
 49. A method as claimed in claim 46, further including:associating a value denoted ψ′_(s) of an evaluating variable with aknown value of a binary status variable; calculating a value denotedψ″_(s) of the evaluating variable that is associated with the oppositebinary outcome of the status variable such that s(ψ″_(s))=

s(ψ′_(s)); storing the values ψ′_(s) and ψ″_(s) for further use in theoperation Measurement in the set point level measurement applicationsand for a material presence detection in the vicinity of the level setpoint and in level switching applications; and updating the valuesψ′_(s) and ψ″_(s) according to a schedule of execution of the BMP.
 50. Amethod as claimed in claim 23, further including: applying the CRMP tomore than one point on the external wall of the vessel; and executing arepetitive CRMP (RCRMP), such that the level of the filling material ismeasured at several points.
 51. A method as claimed in claim 50, furtherincluding: locating a plurality of points along a vertical axis on theexternal wall of the vessel; applying a Basic Measurement Procedure(BMP) sequentially to each point of the plurality of points beginningfrom a starting position on the vessel's external wall toward an endingposition on the vessel's external wall until the following condition issatisfied:∃j∈[1,m]⊂

: ψ_(j)(t)∈(ψ*₁,ψ*₂)

ψ(t)=ψ_(j)(t), wherein, ψ_(j)(t) denotes an evaluating variable for aj-th execution of the BMP; ψ*₁, ψ*₂ and K* respectively denote upper andlower saturation points and a gain factor of an aggregated transferoperator of a distributed measuring system or device; and calculatingthe level by the following formulas:y*=(ψ* ₁−ψ*₂)/K*y _(j)(t)=[ψ(t)−ψ⁰ ]/K*y(t)=(j−1)y*±y _(j)(t)L _(fm) =H−y(t)

starting position is in the upper half of vesselL _(fm) =y(t)

starting position is in the lower half of vessel wherein, y* denotes aspread distance corresponding with a linear part of the distributedmeasuring system's transfer operator; H denotes a height of the startingposition, and the “+” in the “±” sign is for a starting point located ina lower half of the vessel and the “−” in the “±” sign is for a startingpoint located in an upper half of the vessel.
 52. A method as claimed inclaim 50, further including: locating a plurality of points along avertical axis on the external wall of the vessel; applying a BasicMeasurement Procedure (BMP) simultaneously to at least two points of theplurality of points beginning from a starting position on the vessel'sexternal wall toward an ending position on the vessel's external walland detecting the ordering number of the point, for which the followingcondition is satisfied:∃j∈[1,m]⊂

: ψ_(j)(t)∈(ψ*₁,ψ*₂)

ψ(t)=ψ_(j)(t); and calculating the evaluating variable's value by theformula:$\left. {{{\left\{ {{\forall{\omega_{i} \in \left\lbrack {\omega_{1},\omega_{2}} \right\rbrack}},{i = \overset{\_}{1,m}}} \right\}\&}\mspace{14mu} t} > t_{0}}\Rightarrow{\psi(t)} \right. = \left. {\sum\limits_{i = 1}^{i = m}{\sin\left( T_{i} \right)}} \right|_{A_{i} \in {\lbrack{A_{1},A_{2}}\rbrack}}$wherein, [ω₁, ω₂] denotes a frequency range satisfying a criterion ofnon-generation of mechanical elastic waves, T_(i) denotes an i-th fullperiod of oscillation observed beginning at a moment t₀.
 53. A method asclaimed in claim 50, for applications with a multi-layer structure ofthe filling material, having layers of a different density, to measuredimensions of each layer of the multi-layer structure in the vessel,further including: applying a repetitive CRMP (RCRMP).
 54. A method asclaimed in claim 21, further including: prior to initializing themechanical oscillation, mounting elements on the vessel's wall forsetting boundary conditions for mechanical oscillation-induced elasticwaves propagating in the vessel, to define a linear part of a levelmeasurement system's static transfer operator.
 55. A method as claimedin claim 21, further including: receiving at least one acoustical signaloriginated by an application of at least one percussion within asequence of operations of a Basic Measurement Procedure (BMP); andcalculating an evaluating variable resulting from the BMP using ameasured mechanical oscillation and a measured acoustical signalassociated with the mechanical oscillation.
 56. A method as claimed inclaim 21, further including: performing the LRMP by executing twooperations wherein the first operation is an operation of calibrationand the second operation is an operation of measurement.
 57. A method asclaimed in claim 56, wherein the operation of calibration includes thesteps of: setting an initial value of the filling material level in thevessel; non-tangentially applying the mechanical oscillation to thevessel's external wall at a predetermined point to initiate a transversewave; capturing an occurrence of the transverse wave at a predeterminedtransverse wave receiving point; and measuring and storing the value ofa time interval denoted ΔT* between the moment of the transverse waveinitiation and the moment of the wave occurrence capturing, such thatthe time interval ΔT* is associated with a distance between the point oftransverse wave initiation and the filling material interface, denotedy*.
 58. A method as claimed in claim 56, wherein the operation ofmeasurement includes the steps of: non-tangentially applying themechanical oscillation to the vessel's external wall at a point of atransverse wave initiation; capturing an occurrence of the transversewave at a predetermined transverse wave receiving point; measuring andstoring a value of a time interval denoted ΔT between the moment of thetransverse wave initiation and the moment of the wave occurrencecapturing, such that the time interval ΔT is associated with a distancebetween the point of transverse wave initiation and the filling materialinterface, denoted y; and calculating the measured level denoted L_(fm),by the formulas: $y = {\frac{\Delta\; T}{\Delta\; T^{*}} \cdot y^{*}}$L_(fm) = H − y − d wherein, d denotes a known distance between a top ofthe vessel and the point of of transverse wave initiation.
 59. A methodas claimed in claim 21, wherein performing the LRMP includes thefollowing steps: arranging for monitoring a presence of a transversewave at a plurality of receiving points on the external wall of thevessel to compensate for possible variations in propagation speed of themonitored waves through the material of the vessel's wall;non-tangentially applying the mechanical oscillation to the vessel'sexternal wall at the point of a transverse wave initiation; capturingthe transverse wave's presence at each wave's receiving point of theplurality of points; measuring and storing each value of a time intervaldenoted ΔT_(i) between a moment of the transverse wave initiation and amoment of the wave capturing at an i-th point of the plurality ofpoints, such that each time interval ΔT_(i) is associated with adistance between the i-th receiving point and the filling materialinterface, denoted y_(i); and calculating the level by solving thefollowing system of algebraic equations of the order m:F(L _(fm) , H, ΔT, d)=0 wherein, L_(fm) denotes the level of fillingmaterial in the vessel; H denotes a height of the vessel; ΔT denotes avector of time intervals between the moment of the transverse waveinitiation and the moment the wave capturing at the i-th point of theplurality of points; d denotes a known distance between a top of thevessel and the point of transverse wave initiation; m denotes the numberof the transverse wave receiving points.
 60. A method as claimed inclaim 59, further including: calculating the measured level by thefollowing formulas:$y = {\frac{\Delta\; T}{{\overset{\_}{\Delta\; T}}^{*}} \cdot \overset{\_}{y^{*}}}$${y^{*} = {n^{- 1}{\sum\limits_{i = 1}^{i = n}\overset{\_}{y_{i}^{*}}}}},{{\Delta\; T^{*}} - {n^{- 1}{\sum\limits_{i = 1}^{i = n}{\overset{\_}{\Delta\; T}}_{i}^{*}}}}$L_(fm) = H − y − d wherein, y* and ΔT* denote an aggregated calibratingdistance and an aggregated calibrating wave travel time obtained bymonitoring the wave's responses captured at n receiving points of theplurality of the transverse wave receiving points and ΔT represents thetransverse wave's travel time along the wall of the vessel.
 61. A methodas claimed in claim 59, wherein an evaluating variable ψ_(L)∈ψ_(L)generated by the LRMP includes a variable ΔT, representing thetransverse wave's travel time along the wall of the vessel, theevaluating variable ψ_(L) being a function of the variable ΔT, such thatψ_(L)=F(ΔT), and a filtering or aggregation or statistical processing isapplied to obtain the evaluating variable for the LRMP.
 62. A method asclaimed in claim 60, further including: calculating the variable ΔT bythe formula:${\Delta\; T} = {m^{- 1}{\sum\limits_{j = 1}^{j = m}{\Delta\; T_{j}}}}$wherein, ΔT_(j) denotes a travel time obtained at j-th measurement inthe series of m measurements.